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Old 28th September 2002, 05:05 AM   #111
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Default Steve's reply on CD format

From Steve's post:

Also, the data doesn't actually exist on the disc in binary, linear PCM form to begin with. Contrary to popular belief, a pit doesn't designate a 1 and a land a 0 (or vice versa). In other words, if the data is 10110 you don't have a pit/land/pit/pit/land.

>> Steve I think you should be more clear here on what you are calling data. I think you mean to say that the raw audio signal isn't encoded as pits and lands. This is true, however a rising edge on a pit is what defines a '1' and a land is a '0'. These '1's and '0's therefore refer to audio encoded with EFM and CIRC.

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Old 28th September 2002, 05:13 AM   #112
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Default Re: "shhhhhhhhhhhhhhhhhhhhhhhhhh"

Quote:
Originally posted by HarryHaller
Absolutley nothing has been discussed about the addition of this extra light souce's effect on jitter, Bit Error Rate, or how hard the servo is having to work in focusing the laser.
My intent was to address the specific technical claims made by YBA in the sidebar.

If you'd care to offer up something on the other things you mentioned, I'd be happy to discuss them.

I've given it some thought and haven't been able to think of any way that the blue light would have any particular effect on jitter, BER, servos, etc.

First, the light's blue. Typically about 430 nm. The photodiodes used in the detection system have their peak sensitivities at or above the 780 nm wavelength of the laser diode so they have significantly less sensitivity down at 430 nm.

Second, the light output from the diode is constant so even if some of it manages to end up striking the photodiodes, I don't see how it would produce any noise to speak of.

Third, the laser system uses interferometry (the depth of the pits on the CD correspond to 1/4 wavelength of the 780 nm laser light accounting for the refraction index of the polycarbonate) to achieve a very high signal-to-noise ratio and a very high contrast level between pit/land transitions.

If you've any alternatives, let's hear 'em.

Quote:
I don't think anyone has scratched the surface of the technical issues involved. I guess denial has always been easier than investigation though.
The only thing I've denied are the patently false technical claims made by YBA.

se
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Old 28th September 2002, 05:38 AM   #113
BrianL is offline BrianL  United States
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Default Truth vs. B.S.

You know, I don't mind Peter (you need a better picture)
or anyone else saying they like the sound of their CD
when bathed in pink, purple, or blue light. I think I'm
becoming more of a grumpy old "objectivist" as I get older,
but I've heard effects from some tweeks that I can't
explain (as well as noticing absolutely ZERO effect from
many, many more...). Let other people try it and eventually
it will sort itself out. I don't track the "high end" rags that
well, but I've not heard much about green markers lately.

HOWEVER, I do get VERY annoyed with things like this
clip from Stereophile, where some supposed guru designer
speaks ex cathedra about the "science" behind some
tweek and it's total unabashed B.S. No possibilty of being
true. And the scary thought is that if he really believe
what hes says, he has no concept how the technology
behind his product works (i.e., how audio bits are encoded
and recorded onto a CD)

Yikes, we are running headlong into a self-referenced
postmodern culture where there is no concept of objective
truth/reality and everything has truth/meaing only if it is
meaningful to me.
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Old 28th September 2002, 05:42 AM   #114
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Default My opinion on why some 'mid-fi' companies use the overhead diode..

I saw a few posts which stated that Magnavox (I believe) has or had a separate LED illuminate the CD. My old Fisher AD-822 has a red LED.

I think that the reason why these 'mid-fi' companies have employed these LEDs is solely for cosmetic purposes. In these products the light from the LED is reflected onto the label side of the disc, not the data side. In a lot of products, the center portion of the CD tray has an around 2 inches of clear plastic which permits the user to see the disc and the light from the LED. When the LED is ON, it is easy to see the disc spinning since the light hitting the disc label produces a strobe effect to the human eye - one source of user feedback that the motor is spinning and playing music. In this scenario, the light from the LED is obstructed from the photodiode by the CD itself.

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Old 28th September 2002, 05:45 AM   #115
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Default Re: Steve's reply on CD format

Quote:
Originally posted by AudioEnthusiast
From Steve's post:

Also, the data doesn't actually exist on the disc in binary, linear PCM form to begin with. Contrary to popular belief, a pit doesn't designate a 1 and a land a 0 (or vice versa). In other words, if the data is 10110 you don't have a pit/land/pit/pit/land.

>> Steve I think you should be more clear here on what you are calling data. I think you mean to say that the raw audio signal isn't encoded as pits and lands. This is true, however a rising edge on a pit is what defines a '1' and a land is a '0'. These '1's and '0's therefore refer to audio encoded with EFM and CIRC.
That's incorrect. That would be the case if the EFM data were NRZ coded (Non Return to Zero). But instead, the EFM data is NRZI coded (Non Return to Zero Inverted). With NRZI coding, the 1s only represent pit/land transitions, while the pits and lands themselves alternately represent 0s.

For example, if the EFM data were:

0100010010001

The 1s are where the pit/land transitions occur. And let's say that we're heading into the first 1 from a land. Then we hit the first 1 which means we have a transition from a land to a pit. The pit represents the 0s until we get to the second 1, where we transition from a pit to a land. After the second 1, the land now represents the 0s until we get to the third one, after which the pit represents the 0s, and so on.

In other words, 1 represents neither a pit nor a land. Merely a transition from one to another, regardless of which one to which other.

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Old 28th September 2002, 06:09 AM   #116
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Default Re: Re: Steve's Reply on CD Format

Steve, I agree, you are right. I should have said a '1' represents a pit only on the rising and falling edges for the EFM data - the signal transitions you referred to. I see this illustrated in a diagram in Pohlmann's book. My bad.

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Old 28th September 2002, 06:23 AM   #117
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Default Re: Re: Re: Steve's Reply on CD Format

Quote:
Originally posted by AudioEnthusiast
Steve, I agree, you are right. I should have said a '1' represents a pit only on the rising and falling edges for the EFM data - the signal transitions you referred to. I see this illustrated in a diagram in Pohlmann's book. My bad.
No problem. And thank you for not taking offense simply because I disagreed.

The main point I was trying to make in my previous post was that there's simply nothing on the disc at an actual binary bit for bit level which means that there's nothing on the disc that equates in any way to the LSB of the actual PCM audio data.

se
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Old 28th September 2002, 06:34 AM   #118
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Steve,

Why error-correction algorithms are used when extracting data from digital medium? As I remeber correctly some companies claim to have superior algorithms allowing their equipment to sound better then other. What makes their algorithms superior?
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Old 28th September 2002, 06:50 AM   #119
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Default This is how I see it

I found this on a usenet post on the same subject,

"Across a typical CD, less than a dozen uncorrected but concealed errors may be expected, and zero or one unconclealed (muted) errors. Concealed errors consist of interpolated values between correct levels, and it's not being very bold to suggest that they are TOTALLY inaudible, consisting as they do of sub-millisecond values of roughly correct amplitude occurring perhaps ten times in an hour of music. So we have for all intents and purposes a perfect data recovery system."

This is inline with my previous knowledge, and what I believe is commonly held as fact. Given the almost perfect accuracy of the recovered data, it seems to me that WHATEVER effect the blue LED has, it is in producing a recovered signal that is LESS ACCURATE than what is typically sent to the DAC. It is, however, apparently pleasing to some people. Maybe in the same way that tubes are preferable to some over SS. I have yet to try it.
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Old 28th September 2002, 06:57 AM   #120
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Default a link to more info

I "think" this is a good reference on error-correction.

http://groups.google.com/groups?selm...&output=gplain
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