MediaTek started the whole price landslide... and now all the chipset makers have been forced to cut corners (and staff!) to keep up. The bulk of production volume comes from these Chinese OEMs who buy their chipsets based on price alone. Manufacturers used to care about quality, but lately, they're not interested. Features are checklist items now... like progressive scan. They don't care if it works well or not, only that they can put the label on the box!
I recall a trip to an Asian OEM about two years ago, to try and convince their senior engineers that our chipset's progressive scan was technically better than a major competitor's chipset (and it was, IMHO). At the time, our sales depended on securing contracts with technical discussions like this. But in the last year or slightly more, the only thing they want to hear is price... technical sales meetings dried right up.
mrfeedback:
The differences in pickup are mainly the laser and photodiode. It mostly boils down to production quality control and tolerances for optical alignments, at least to my understanding. (You understand, I didn't work on pickup design, I just got to see how well they worked in-system...). But there are some problems that come up... lasers burn out because of bad design or poor power control ciruitry. RF signal can be weak or noisy if the analog circuits in the pickup aren't good. Same thing with various error signals that help with focus and tracking. One key thing that many people don't take into consideration is that an optical pickup (OPU), and the associated front-end circuitry is predominantly high-frequency analog stuff. A lot of cheap OEM designs haven't had all of the analog circuitry properly optimized. Even simple things like bias resistors and reference voltages can get screwed up, just because of the sheer number of different OPU models and RF preamplifier ICs available - each combination of OPU+RF amp requires different discrete circuitry to work together, and it must all be meticulously optimized. There's also a motor driver IC, which needs good S/N performance so that the feedback loops can be tightly controlled, and the cheap chips are just plain noisy. There's a myriad of little things that need care and attention in a front-end circuit. Layout is very very important here too. And, of course, you'd better believe that the motors will have an influence on servo loop performance too. Sled gearing sometimes has some slop in it, which leaves a dead-zone in the servo control, and an ambiguity during seek operations, which can drastically slow them down. Anyway, I could ramble on, but what's the point. Cheap is cheap. You get what you pay for. Joe six-pack just hasn't figure out yet that his little $39 special is a piece of junk... they haven't been on the market long enough for the masses to learn their lesson. Soon enough, the market will reach saturation, and people will begin "upgrading" to better models as they replace their crappy ones. Then, I hope, we'll see the return of some quality. Of course, HD-DVD will be making inroads by then...
milwood: actually, it wasn't Cirrus, it was C-Cube, my ex-employer. C-Cube created the VCD standard, and pioneered much of the MPEG encoding tech for professional video studios. Today, C-Cube is owned by LSI Logic, and has moved out of the DVD chipset biz, but should be a major player in DVD recorders, which is set to be the next Big Thing(tm). Cirrus has always seemed to be just an "also-ran" in the DVD chipset world. I did a certain amount of competitive product analysis, and have seen pretty much the full gamut of chipsets, but never came across a Cirrus DVD chipset. Zoran, however, has held out fairly well over the last few years. It seems their cost cutting has been more successful than others, and they've more or less retained their Toshiba business. But if you ask me, their chipset is pretty ho-hum.
I recall a trip to an Asian OEM about two years ago, to try and convince their senior engineers that our chipset's progressive scan was technically better than a major competitor's chipset (and it was, IMHO). At the time, our sales depended on securing contracts with technical discussions like this. But in the last year or slightly more, the only thing they want to hear is price... technical sales meetings dried right up.
mrfeedback:
The differences in pickup are mainly the laser and photodiode. It mostly boils down to production quality control and tolerances for optical alignments, at least to my understanding. (You understand, I didn't work on pickup design, I just got to see how well they worked in-system...). But there are some problems that come up... lasers burn out because of bad design or poor power control ciruitry. RF signal can be weak or noisy if the analog circuits in the pickup aren't good. Same thing with various error signals that help with focus and tracking. One key thing that many people don't take into consideration is that an optical pickup (OPU), and the associated front-end circuitry is predominantly high-frequency analog stuff. A lot of cheap OEM designs haven't had all of the analog circuitry properly optimized. Even simple things like bias resistors and reference voltages can get screwed up, just because of the sheer number of different OPU models and RF preamplifier ICs available - each combination of OPU+RF amp requires different discrete circuitry to work together, and it must all be meticulously optimized. There's also a motor driver IC, which needs good S/N performance so that the feedback loops can be tightly controlled, and the cheap chips are just plain noisy. There's a myriad of little things that need care and attention in a front-end circuit. Layout is very very important here too. And, of course, you'd better believe that the motors will have an influence on servo loop performance too. Sled gearing sometimes has some slop in it, which leaves a dead-zone in the servo control, and an ambiguity during seek operations, which can drastically slow them down. Anyway, I could ramble on, but what's the point. Cheap is cheap. You get what you pay for. Joe six-pack just hasn't figure out yet that his little $39 special is a piece of junk... they haven't been on the market long enough for the masses to learn their lesson. Soon enough, the market will reach saturation, and people will begin "upgrading" to better models as they replace their crappy ones. Then, I hope, we'll see the return of some quality. Of course, HD-DVD will be making inroads by then...
milwood: actually, it wasn't Cirrus, it was C-Cube, my ex-employer. C-Cube created the VCD standard, and pioneered much of the MPEG encoding tech for professional video studios. Today, C-Cube is owned by LSI Logic, and has moved out of the DVD chipset biz, but should be a major player in DVD recorders, which is set to be the next Big Thing(tm). Cirrus has always seemed to be just an "also-ran" in the DVD chipset world. I did a certain amount of competitive product analysis, and have seen pretty much the full gamut of chipsets, but never came across a Cirrus DVD chipset. Zoran, however, has held out fairly well over the last few years. It seems their cost cutting has been more successful than others, and they've more or less retained their Toshiba business. But if you ask me, their chipset is pretty ho-hum.
I think it's complete BS. Same with "sonic-enhancing" blue LEDs shining on the disc. I know enough about how optical pickups and the associated circuitry work to be severly skeptical of almost every argument I've heard in their favour. I chalk it up to listener psychology. That said, I haven't done much research or thinking on the subject, so perhaps there's some obscure mechanism of operation I've overlooked. There doesn't seem to be much, if any, solid scientific research on the matter, anyway. Proper double-blind testing would be in order, as would serious technical investigation to correlate any audible effects with measurable parameters... maybe if I'm bored, I'll have a look at mrfeedback's article on cd pens.
This is one of those things I hate to admit works, but I have seen it proven with a error-rate detector that the green pen thing can work..... but not always. One of my friends showed this to me about 8 years ago when working on CD-ROMS. For brand new CD's on a good CD-ROM drive, the effect was minimal, however if the disk was a bit "hazed" from physical abuse, it seemed to make a significant difference. However, on some of the cheaper CD-ROM drives, it sometimes made it better, and sometimes worse! He was not looking at jitter, so I can't make any specific comments on that.
I don't profess to have experience in CD\DVD pickups, but I have a fair amount of experience in optical detectors. One theory on why the blue LED "may" work is that it may actually bias the detector into a better operational range. That said, it may not matter if it is blue or whatever. Blue may work best because very little light is likely to get through the optical filter as opposed to another color closer to the optical cut-off. That said and done, any light that gets through may increase the noise level.
Alvaius
I don't profess to have experience in CD\DVD pickups, but I have a fair amount of experience in optical detectors. One theory on why the blue LED "may" work is that it may actually bias the detector into a better operational range. That said, it may not matter if it is blue or whatever. Blue may work best because very little light is likely to get through the optical filter as opposed to another color closer to the optical cut-off. That said and done, any light that gets through may increase the noise level.
Alvaius
There's jitter and there's jitter
There seems to be some confusion about jitter. As far as I can
see there are two different and unrelated phenomenae
referred to as jitter. The first is clock jitter in the AD and DA
conversions, which has been discussed extensively and it is
also straightforward from theory that such jitter can affect the
final analog signal. The other type of jitter, which Eric talked
about previously in the thread, is jitter in the process of
reading/writing. There is some jitter when reading the disc and
there is some jitter when writing the disc, where the latter
will be recorded in the digital data and thus add to the jitter
of the reading process itself. However, it is important to note
that this second type of jitter has nothing to do with the first
type, since the data is buffered and it is only the jitter of the
clock reading the buffer that affects the analog signal. The
second type of jitter can, however, cause data corruption of
the digital signal if it is serious enough. That is, it may cause
read errors, which can affect the sound but in a different way
than clock jitter does.
There seems to be some confusion about jitter. As far as I can
see there are two different and unrelated phenomenae
referred to as jitter. The first is clock jitter in the AD and DA
conversions, which has been discussed extensively and it is
also straightforward from theory that such jitter can affect the
final analog signal. The other type of jitter, which Eric talked
about previously in the thread, is jitter in the process of
reading/writing. There is some jitter when reading the disc and
there is some jitter when writing the disc, where the latter
will be recorded in the digital data and thus add to the jitter
of the reading process itself. However, it is important to note
that this second type of jitter has nothing to do with the first
type, since the data is buffered and it is only the jitter of the
clock reading the buffer that affects the analog signal. The
second type of jitter can, however, cause data corruption of
the digital signal if it is serious enough. That is, it may cause
read errors, which can affect the sound but in a different way
than clock jitter does.
alvaius:
Consider that the photodiodes are imaging a very tiny laser spot (on the order of a few microns in diameter) over most of their surface area. Almost the full power of the laser (minus reflective and transmissive losses) is focused on this tiny spot, so you may begin to understand that the ratio of laser light to ambient light reaching the photodiodes is quite large. This particular fact makes possible the disc detection/discrimination and focus search operations. I don't think the blue LED will have significant effect on the photodiode biasing. At one time, I'd planned to actually go into the lab with a blue LED and see what I could measure, but never got around to doing more than a quick-n-dirty trial, which turned up nothing useful. As far as I could tell, none of the major signals were affected by the presence of the LED, but of course this was not a very scientific or thorough test.
What I have seen, and heard reported (well before green pens and blue LEDs became fashionable), is camera flashes upsetting playback. Now whether this is due to electromagnetic interference from the flash electronics discharging, and interfering directly with the RF circuits in the pickup, or whether it's due to intense light entering the photosystem, I don't know... but food for thought, anyway. People naturally jumped to the conclusion that it was caused by the flash of light, and hence started focusing attention on optical effects. I personally lean in the direction of an EM burst interfering with the RF circuitry, which isn't always well shielded. It would be nice to believe that there is a universal "fix" (as though something needs fixing ) for every CDP out there, but in reality, every design will react differently to EM interference and the presence of ambient light or other optical differences.
Consider that the photodiodes are imaging a very tiny laser spot (on the order of a few microns in diameter) over most of their surface area. Almost the full power of the laser (minus reflective and transmissive losses) is focused on this tiny spot, so you may begin to understand that the ratio of laser light to ambient light reaching the photodiodes is quite large. This particular fact makes possible the disc detection/discrimination and focus search operations. I don't think the blue LED will have significant effect on the photodiode biasing. At one time, I'd planned to actually go into the lab with a blue LED and see what I could measure, but never got around to doing more than a quick-n-dirty trial, which turned up nothing useful. As far as I could tell, none of the major signals were affected by the presence of the LED, but of course this was not a very scientific or thorough test.
What I have seen, and heard reported (well before green pens and blue LEDs became fashionable), is camera flashes upsetting playback. Now whether this is due to electromagnetic interference from the flash electronics discharging, and interfering directly with the RF circuits in the pickup, or whether it's due to intense light entering the photosystem, I don't know... but food for thought, anyway. People naturally jumped to the conclusion that it was caused by the flash of light, and hence started focusing attention on optical effects. I personally lean in the direction of an EM burst interfering with the RF circuitry, which isn't always well shielded. It would be nice to believe that there is a universal "fix" (as though something needs fixing
) for every CDP out there, but in reality, every design will react differently to EM interference and the presence of ambient light or other optical differences.to just add to chad's point, doesn't the laser pick-up have very limited bandwidth and very close focus distance?
so you have to use the same wavelength (mostly red) or focus on the exactly point for the light to be seen by the laser diode. Both are pretty hard to do.
the close focus distance is useful so that smears on the disk or minor cuts don't bother the laser pick-up.
so you have to use the same wavelength (mostly red) or focus on the exactly point for the light to be seen by the laser diode. Both are pretty hard to do.
the close focus distance is useful so that smears on the disk or minor cuts don't bother the laser pick-up.
Hi Chad,
Thanks for your further info.
My question was mainly related to why pickups fail.
I have replaced hundred of faulty pickups (mostly KSS types) in audio cdp's in my time, but have never been able to get a definitive answer on why/how they fail.
I have had several pickups with no laser light output, but the by far majority seemed mechanically ok, but would either not track at all, or would skip very easily despite optimising servo adjustments.
Notable is that the RF signal is usually quite noisey/jittery with defective/borderline pickups, but then again new pickups that work perfectly fine can exhibit noisey RF output also.
Eric.
Thanks for your further info.
My question was mainly related to why pickups fail.
I have replaced hundred of faulty pickups (mostly KSS types) in audio cdp's in my time, but have never been able to get a definitive answer on why/how they fail.
I have had several pickups with no laser light output, but the by far majority seemed mechanically ok, but would either not track at all, or would skip very easily despite optimising servo adjustments.
Notable is that the RF signal is usually quite noisey/jittery with defective/borderline pickups, but then again new pickups that work perfectly fine can exhibit noisey RF output also.
Eric.
Well, lasers just get old and wear out - like a lightbulb. Eventually, they just burn out. The photodiodes can also degrade over time... lower sensitivity and whatnot. I don't really know all the details myself, as my company didn't make pickups. But, from my understanding, the laser usually has the lowest MTBF. This is also affected by the automatic power control (APC) circuit that servo-controls the laser's light output level. As the laser ages, it's light output falls, and it gets driven harder and harder by the APC to try and keep the light output constant. At some point, the APC circuit may just saturate, and so while the laser is still operating, it's output is too low, leading to poor tracking and focus, disc detection etc.
Older CDPs also relied on purely analog servo loops, and were subject to problems of component tolerances and aging leading to drifting values and part failures (caps, resistors and opamps). Nowadays it's all digital - the RF goes through a high speed A-D, gets processed in DSP, then a DAC spits out the signals to control the tracking and focus coils, sled motor, and spindle. A handful of not-so-critical passives are used to filter signals for the ADCs or DACs. So DSP has taken a big bite out of the component aging problem. I have seen issues related to DAC and ADC performance, though these are generally not considered a "wear item" unless the silicon gets exposed to ESD or some other damaging conditions during it's lifecycle.
It's worth noting that most consumer grade servo loops are a bit marginal in terms of performance, even the best ones. Ever since I first started working with DVD front-ends, I have always been amazed that they work so well for such noisy circuits. The precision required for tracking and focus is quite remarkable! But, profit margin considerations will always ensure that the parts used are just good enough to do the job, without unnecessary cost related to improving that performance beyond what is strictly necessary for proper function. There's a sweet spot, where everything is tuned at manufacture time, and all is well within that sweet spot. But, stray too far, and focus, tracking and spindle control get a bit grouchy, as I'm sure you're well aware. Manufacturers could use better lasers, better optics, better photodiodes, better RF chips and motor drivers etc., but would the average consumer ever know the difference? Not counting performance with damaged discs, the pickup either works, or it doesn't. There's not much in between.
Speaking of servo loop performance, and tying that back to the magic felt pen / blue LED thing, I think a far greater benefit can be realized with improved transport mechanics - simply making the tracking and focus easier. Ultimately, this boils down to vibration control... low vibration (read: quiet) motors and smooth running ball bearings, tight tolerance gearing, rigid frame to hold everything solidly in place and damp resonances, and (i think often overlooked) aerodynamics around the spinning disc.
Older CDPs also relied on purely analog servo loops, and were subject to problems of component tolerances and aging leading to drifting values and part failures (caps, resistors and opamps). Nowadays it's all digital - the RF goes through a high speed A-D, gets processed in DSP, then a DAC spits out the signals to control the tracking and focus coils, sled motor, and spindle. A handful of not-so-critical passives are used to filter signals for the ADCs or DACs. So DSP has taken a big bite out of the component aging problem. I have seen issues related to DAC and ADC performance, though these are generally not considered a "wear item" unless the silicon gets exposed to ESD or some other damaging conditions during it's lifecycle.
It's worth noting that most consumer grade servo loops are a bit marginal in terms of performance, even the best ones. Ever since I first started working with DVD front-ends, I have always been amazed that they work so well for such noisy circuits. The precision required for tracking and focus is quite remarkable! But, profit margin considerations will always ensure that the parts used are just good enough to do the job, without unnecessary cost related to improving that performance beyond what is strictly necessary for proper function. There's a sweet spot, where everything is tuned at manufacture time, and all is well within that sweet spot. But, stray too far, and focus, tracking and spindle control get a bit grouchy, as I'm sure you're well aware. Manufacturers could use better lasers, better optics, better photodiodes, better RF chips and motor drivers etc., but would the average consumer ever know the difference? Not counting performance with damaged discs, the pickup either works, or it doesn't. There's not much in between.
Speaking of servo loop performance, and tying that back to the magic felt pen / blue LED thing, I think a far greater benefit can be realized with improved transport mechanics - simply making the tracking and focus easier. Ultimately, this boils down to vibration control... low vibration (read: quiet) motors and smooth running ball bearings, tight tolerance gearing, rigid frame to hold everything solidly in place and damp resonances, and (i think often overlooked) aerodynamics around the spinning disc.
Thanks again........
I only ever had a couple of pickups with no light output, and mostly all others looked to have normal light output level.
The few that did not were able to be adjusted to give normal light output level and RF level.
I found plenty of pickups where the RF output (HF signal) looked fine but would not work in any machine.
Replacing the pickup in these machines cured the problems.
I have also repaired plenty of cdp's by resoldering the servo stages (particularly SMD chips) even though the joints looked fine by visual inspection.
I agree that it seems a wonder that some machines work at all despite the electrically noisey environment and doubtful power and grounding techniques typically used.
A comment made to me regarding modern WM type players with anti-shock buffer memory was that this allowed usage of lousy pickups because of multiple reads - switch the shock buffer to off and these mistrack at the merest bump.
Just some Info from the servicing (20+ years) side.....
Q - do all DVD players run at multiple disc speed when playing audio discs ?.
Eric.
I only ever had a couple of pickups with no light output, and mostly all others looked to have normal light output level.
The few that did not were able to be adjusted to give normal light output level and RF level.
I found plenty of pickups where the RF output (HF signal) looked fine but would not work in any machine.
Replacing the pickup in these machines cured the problems.
I have also repaired plenty of cdp's by resoldering the servo stages (particularly SMD chips) even though the joints looked fine by visual inspection.
I agree that it seems a wonder that some machines work at all despite the electrically noisey environment and doubtful power and grounding techniques typically used.
A comment made to me regarding modern WM type players with anti-shock buffer memory was that this allowed usage of lousy pickups because of multiple reads - switch the shock buffer to off and these mistrack at the merest bump.
Just some Info from the servicing (20+ years) side.....
Q - do all DVD players run at multiple disc speed when playing audio discs ?.
Eric.
That's odd, indeed. If you're actually getting an RF signal, and A - F diode signals all look OK, then i see no reason it shouldn't work... i mean, in order to have an RF signal at all, the focus, tracking and spindle servo loops need to be locked. So that's a bit of a mystery. Perhaps it has something to do with the actuator coils / suspension wearing out. I dunno... just a random thought.
Regading the anti-shock models, that doesn't surprise me at all.
No. In fact, every DVD player I've encountered reverts to plain-jane 1x playback, just like an ordinary CDP. Sidenote: most DVD players have a separate laser just for CD, but cheap players skip this, and use one laser for both DVD and CD. Of course, it won't be the proper wavelength for one or maybe even both types of disc. Back to the point: the reason nobody does higher read speeds is that CD discs don't have any kind of physical data addressing built in, like HDDs or DVDs do. This makes it hard to realign the data streams if there's a jump during playback... you don't know where you are, or where you were in the data stream. Hence, when a CD skips, the playback can resume from just about any random point in the adjacent data. Yes, there's a timecode in Q-subchannel, but that's not very reliable or useful, so it's just ignored. At the root, CD playback almost always relies on a servo loop controlling the spindle speed, in order to keep the RF signal locked to a PLL, and the data flows at exactly 1x... straight to the DACs (or maybe through a buffer).
In contrast, DVD playback is done at higher disc speed than necessary, because the data packets all contain physical addresses that allow easy realignment of the data. When the read-channel buffer is full, the OPU jumps backward and re-reads some data. The DVD front-end is thus slave to the decoder chip, which requests data from addresses as it needs that data, and lets the front end chipset figure out how to deliver it, just like a hard drive.
jittery talk
I'm out of TIME for this jittery talk now, but I have some CDR discs recorded several years ago on a first generation HP x2 CDR drive, and I can hear it's not perfect.
Bass is not tight.
I've bought some original CDs of those that I have recorded long ago and the difference is amazing.
If I copy a CD now, at home, it will be very difficult to distinguish from the original, but on a cheap CDR drive and/or disc and mainly if you record at more than 4x,you'll muck up the sound.
Of cource, you can only hear the effect playing the disc on a good source.
Low Jitter.
My CDP has an LC-audio XO clock, from 1999 (I must be one of the oldest foreign customers of the LC clock).
Bass is tight, soundstage very good.
If it's not, something's wrong.
I'm out of TIME for this jittery talk now, but I have some CDR discs recorded several years ago on a first generation HP x2 CDR drive, and I can hear it's not perfect.
Bass is not tight.
I've bought some original CDs of those that I have recorded long ago and the difference is amazing.
If I copy a CD now, at home, it will be very difficult to distinguish from the original, but on a cheap CDR drive and/or disc and mainly if you record at more than 4x,you'll muck up the sound.
Of cource, you can only hear the effect playing the disc on a good source.
Low Jitter.
My CDP has an LC-audio XO clock, from 1999 (I must be one of the oldest foreign customers of the LC clock).
Bass is tight, soundstage very good.
If it's not, something's wrong.
HiFiZen, perhaps you can answer this question?
A few posts back you stated that the DVD is actually read faster than the data is needed. I knew this was true for movies, but have not been able to confirm it for DVD-Audio/SACD.
I have done some rough jitter measurements on CD-Audio and DVD-Audio on my Pioneer and JVC DVD-Audio players as well as a friends Panasonic. In all cases, the jitter on the clocks for DVD-Audio was better, substantially on the JVC. This sort of leads me to believe that the DVD players are buffering even on DVD-Audio.
One of the reasons I have asked is that I have sort of abandoned building an oversampling CD player and plan to put that effort into upgrading a DVD player. I plan to take my CDs and up-sampling them on the PC (playing around with the algorithms), and then burn them to DVD-Audio disks.
Alvaiusdesign program].
A few posts back you stated that the DVD is actually read faster than the data is needed. I knew this was true for movies, but have not been able to confirm it for DVD-Audio/SACD.
I have done some rough jitter measurements on CD-Audio and DVD-Audio on my Pioneer and JVC DVD-Audio players as well as a friends Panasonic. In all cases, the jitter on the clocks for DVD-Audio was better, substantially on the JVC. This sort of leads me to believe that the DVD players are buffering even on DVD-Audio.
One of the reasons I have asked is that I have sort of abandoned building an oversampling CD player and plan to put that effort into upgrading a DVD player. I plan to take my CDs and up-sampling them on the PC (playing around with the algorithms), and then burn them to DVD-Audio disks.
Alvaiusdesign program].
HiFiZen,
W.R.T. the small spot size and ambient versus laser light, you are thinking from the perspective of the pits. However, when you consider ambient light, you must think from the surface of the CD as well (or predominantly depending on surface condition, ambient light angle, etc).
Remember that the reflective pits are covered by over 1mm of plastic. The pits and focusing spot may be on the order of 1/2*2uM at the surface of the pits, however, at the surface of the disk, the spot is more on the order of 1/2-1mm. That is starting to get fairly large. This is one of the main reasons why CDs are not that susceptible to small scratches.
When we think of a spot size of 1/2-1mm, the possibility for ambient light can become significant.
Alvaius
p.s. I would still lean towards the RF for the photoflash, however, photoflashes have huge optical power levels (not energy). A good camera flash can output several joules in 10's of microseconds for a power level in the 100,000 watt+ range.
W.R.T. the small spot size and ambient versus laser light, you are thinking from the perspective of the pits. However, when you consider ambient light, you must think from the surface of the CD as well (or predominantly depending on surface condition, ambient light angle, etc).
Remember that the reflective pits are covered by over 1mm of plastic. The pits and focusing spot may be on the order of 1/2*2uM at the surface of the pits, however, at the surface of the disk, the spot is more on the order of 1/2-1mm. That is starting to get fairly large. This is one of the main reasons why CDs are not that susceptible to small scratches.
When we think of a spot size of 1/2-1mm, the possibility for ambient light can become significant.
Alvaius
p.s. I would still lean towards the RF for the photoflash, however, photoflashes have huge optical power levels (not energy). A good camera flash can output several joules in 10's of microseconds for a power level in the 100,000 watt+ range.
alvaius:
Yes, all DVD and DVD-in-disguise (SACD) media is generally treated the same by the front end circuitry. From the point of view of the servo DSP and associated control logic, it doesn't much care what particular data is on the disc - all it sees is the same basic DVD structure at the lowest level. It's up to the back-end (decoder chip) to decide what kind of content it's dealing with, and handle the data accordingly. So only very rarely will you see any difference in how a front-end handles DVD-V vs. DVD-A vs. SACD. Try this test: pop in a DVD-A or better yet, an SACD and start it playing. Then mute your preamp and press your ear to the front of the player. Depending on the mechanism, you should be able to hear little clicks as the laser head jumps back... on my sony NS-500V, the little clicks occur at roughly a 4 - 6 Hz repetition rate, with significant "jitter". You may hear a different rate, depending on the front-end's buffer depth and other factors.
You also raise an interesting point regarding the size of the laser spot on the disc surface. However, your logic is unfortunately flawed... The lens system works just like a camera lens. To continue with this analogy, imagine the photodiodes (very tiny) to be a single tiny grain of dye / silver halide on a piece of film behind the lens. If the lens is properly focused, the laser spot will be a sharp point on the film, just the right size to cover a single grain of dye (in this case, our photodiodes), and we get a good RF signal to decode into data. Anything in the "scene" either in front or behind the plane of focus becomes a large blurry spot on the film plane, thus distributing it's energy over a much larger area than a single grain of dye. This is why scratches and blue light reflected from the surface will not focus to a point concentrated on the photodiodes... both will have a large circle of confusion (out of focus at the film plane). Hence, the energy density will still be very low compared to the laser, which is focused sharply on the photodiodes only. Also, I should point out that the lens system for an OPU has a very large effective aperture. This gives it a very very shallow "depth of field", to use photographic terms.
That was a bit of a rough explanation, but I hope you understand what I meant. The point is that not all light that enters the lens will be focused to a pinpoint on the photodiodes. The large spot on the surface of the disc will become a large spot at the other end of the lens, covering an area much larger than the photodiodes.
Yes, all DVD and DVD-in-disguise (SACD) media is generally treated the same by the front end circuitry. From the point of view of the servo DSP and associated control logic, it doesn't much care what particular data is on the disc - all it sees is the same basic DVD structure at the lowest level. It's up to the back-end (decoder chip) to decide what kind of content it's dealing with, and handle the data accordingly. So only very rarely will you see any difference in how a front-end handles DVD-V vs. DVD-A vs. SACD. Try this test: pop in a DVD-A or better yet, an SACD and start it playing. Then mute your preamp and press your ear to the front of the player. Depending on the mechanism, you should be able to hear little clicks as the laser head jumps back... on my sony NS-500V, the little clicks occur at roughly a 4 - 6 Hz repetition rate, with significant "jitter".
You may hear a different rate, depending on the front-end's buffer depth and other factors.You also raise an interesting point regarding the size of the laser spot on the disc surface. However, your logic is unfortunately flawed... The lens system works just like a camera lens. To continue with this analogy, imagine the photodiodes (very tiny) to be a single tiny grain of dye / silver halide on a piece of film behind the lens. If the lens is properly focused, the laser spot will be a sharp point on the film, just the right size to cover a single grain of dye (in this case, our photodiodes), and we get a good RF signal to decode into data. Anything in the "scene" either in front or behind the plane of focus becomes a large blurry spot on the film plane, thus distributing it's energy over a much larger area than a single grain of dye. This is why scratches and blue light reflected from the surface will not focus to a point concentrated on the photodiodes... both will have a large circle of confusion (out of focus at the film plane). Hence, the energy density will still be very low compared to the laser, which is focused sharply on the photodiodes only. Also, I should point out that the lens system for an OPU has a very large effective aperture. This gives it a very very shallow "depth of field", to use photographic terms.
That was a bit of a rough explanation, but I hope you understand what I meant. The point is that not all light that enters the lens will be focused to a pinpoint on the photodiodes. The large spot on the surface of the disc will become a large spot at the other end of the lens, covering an area much larger than the photodiodes.
hifiZen,
My god, now you are asking me to turn on my optics brain.....
I do, completely see your logic [same logic as if you are taking a picture through a window, get the camera as close to the window as possible so you don't see the dirt on the window], however, I am not sure I completely agree. I think I agree more with you than with myself, though, especially if the effective aperture is large.... yep, blue/ambient should not matter. There will be some dependance on how the light reflects off the surface. If the reflection is diffuse, or essentially spherical radiation, then you are 100% correct. However, if the reflection is specular and the source is far enough away, then you have what is essentially a collimated beam pointing possibly (but not likely) pointing into the lens. [If that sounds really confusing, good, because I confused myself.... think of it more from a ray-tracing standpoint]. However, since people generally mount the blue LED parallel to the disk surface, most of the light should just bounce off.... so you still must be right.
Being a reformed skeptic (ever since I heard the difference between two analog audio cables, not to mention seeing green marker on a disk actually effect bit error rates with my very own eyes), I try to look for ways that something could work before completely dispelling it. You sound very familiar with these optical systems. Is there anyway that light could be "leaking" into the system? The only way I could see a blue LED "helping" would be to bias the detector, so I am trying to think of how the light could get in and do this.
Alvaius
My god, now you are asking me to turn on my optics brain.....
I do, completely see your logic [same logic as if you are taking a picture through a window, get the camera as close to the window as possible so you don't see the dirt on the window], however, I am not sure I completely agree. I think I agree more with you than with myself, though, especially if the effective aperture is large.... yep, blue/ambient should not matter. There will be some dependance on how the light reflects off the surface. If the reflection is diffuse, or essentially spherical radiation, then you are 100% correct. However, if the reflection is specular and the source is far enough away, then you have what is essentially a collimated beam pointing possibly (but not likely) pointing into the lens. [If that sounds really confusing, good, because I confused myself.... think of it more from a ray-tracing standpoint]. However, since people generally mount the blue LED parallel to the disk surface, most of the light should just bounce off.... so you still must be right.
Being a reformed skeptic (ever since I heard the difference between two analog audio cables, not to mention seeing green marker on a disk actually effect bit error rates with my very own eyes), I try to look for ways that something could work before completely dispelling it. You sound very familiar with these optical systems. Is there anyway that light could be "leaking" into the system? The only way I could see a blue LED "helping" would be to bias the detector, so I am trying to think of how the light could get in and do this.
Alvaius
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