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Old 28th September 2002, 02:12 AM   #101
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Quote:
Originally posted by Peter Daniel

You must be kidding here, or you never played with LEDs.
Remarks like this make me thing I'm in a twighlight zone.
Why? I am not sure I understand exactly what are trying to
say here. I am not protesting against your claims that it makes
a difference to add a LED. I am only claiming that it cannot
affect only the LSBs of the data stream, so there must be
some other kind of optical phenomen at play here.

But you're right that I haven't tried the LED trick with CD players.
Probably will some day, but I am bit lazy and quite a bit of
a theoritician, so I'll probably try to convince my more tweakprone
friend to try it out first on his brand new SACD player before I
give it a try myself.

Quote:
So what time is in Sweden now? [/B]
About four o'clock in the morning
How didi this happen??
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Old 28th September 2002, 02:14 AM   #102
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WARNING! This is non-factual information, approach with caution.
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Old 28th September 2002, 02:18 AM   #103
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Quote:
Originally posted by Christer


Why? I am not sure I understand exactly what are trying to
say here. I am not protesting against your claims that it makes
a difference to add a LED. I am only claiming that it cannot
affect only the LSBs of the data stream, so there must be
some other kind of optical phenomen at play here.

I was trying to say that it's impossible to synchronise the LED this way. Everything occurs too fast.

LSB is "weaker" than other bits, that's why it benefits from added energy (by noise). That's what LED does.

The other bits are not affected neither by noise nor by daylight.
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Old 28th September 2002, 02:25 AM   #104
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Sorry Peter, I still don't buy it. All the examples they bring up
for comparison are analog signals/systems, which is quite a
different thing. Doing it on the digital side requires that you
can control which bits are affected. BTW, even if possible you
would only benefit from this if using a 16-bit non-oversampling
DAC I guess. In all other cases you would get much better result
adding noise in later stages. I feel I am stepping out into
deeper water in the last sentences, so others may have a
different opinion here.

BTW, the clock was even 4:40 in the morning.
See, I am too tired to even know what time it is.

I'd better try to sleep on this issue, and I am sure there will
be others around tomorrow to provide more detailed and
refined opnions on this.
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Old 28th September 2002, 02:34 AM   #105
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Quote:
Originally posted by Peter Daniel


I was trying to say that it's impossible to synchronise the LED this way. Everything occurs too fast.

LSB is "weaker" than other bits, that's why it benefits from added energy (by noise). That's what LED does.

The other bits are not affected neither by noise nor by daylight.
OK, yes I also think it would be impossible or at least very
difficult to synchronize the LED. I was just trying to feed
you a last chance of hope for the theory.

I am sorry Peter, but I don't think you quite understand what
digital data is. All bits, including error correction bits etc. have
exactly the same "weight" in the digital data stream. It is only
in the conversion into analog that the bits have different
weights. On the CD, each bit has exaclty the same chance as
any other bit to be affected by the noise. A bit is either 1 or 0,
there are no intermediate values. A 1 in the MSB is exactly the
same thing as a 1 in the LSB, so they are affected in exactly the
same way. I can see no way you could affect the LSBs more
than any other bits, unless you manage to synchronise the
LED. However, if you can come up with convincing arguments
to the contrary I will reconsider my standpoint.
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Old 28th September 2002, 02:43 AM   #106
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Quote:
Originally posted by Christer


On the CD, each bit has exaclty the same chance as
any other bit to be affected by the noise. A bit is either 1 or 0,
there are no intermediate values. A 1 in the MSB is exactly the
same thing as a 1 in the LSB, so they are affected in exactly the
same way. I can see no way you could affect the LSBs more
than any other bits
You are right about the bits on CD. What we are talking here are the bits which are in a "transition process" from CD to the processor. I would imagine they are subject to a different pattern of behaviour.
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Old 28th September 2002, 02:45 AM   #107
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Quote:
Originally posted by Christer
BTW, even if possible you
would only benefit from this if using a 16-bit non-oversampling
DAC I guess. In all other cases you would get much better result
adding noise in later stages. I feel I am stepping out into
deeper water in the last sentences, so others may have a
different opinion here.

It seems that people who use non-oversampling DACs don't notice an improvement.

What can you suggest for adding noise in later stages?
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Old 28th September 2002, 03:18 AM   #108
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Quote:
Originally posted by Peter Daniel
LSB is "weaker" than other bits, that's why it benefits from added energy (by noise). That's what LED does.
The LSB is a bit the same as every other bit. And no bit requires any more or less "energy" than any other bit. The LSB is only "weaker" in a purely mathematically symbolic sense. It simply denotes the bit whose change represents the smallest change possible. That's it. It's just a symbolic weighting factor.

Remember the "decimal place" system when you were in school? You had the 1s decimal place, the 10s decimal place, the 100s decimal place, etc? Well the 1s decimal place is akin to the LSB. You can call it the Least Significant Digit rather than the Least Significant Bit. It's purely symbolic. No digit is any different from any other digit except symbolically.

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.

The data is encoded on the disc in what's called Eight-to-Fourteen Modulation (EFM) and exists as a series of pits/lands of 9 varying lengths, designated 3T, 4T, 5T, 6T, 7T, 8T, 9T 10T and 11T. The shortest pit/land length is between 0.833 and 0.972 um, and the longest is between 3.054 - 3.56 um.

The transition from a pit to a land or a land to a pit is determined by a logical 1 in the EFM data. The EFM data is encoded such that no less than two or no more than ten zeros follow any 1/0 or 0/1 transition.

Since 1/0 or 0/1 transitions are purely a function of the EFM data, and have nothing to do with LSBs, there's simply nothing on the actual disc that has any direct correlation to the actual LSB of the PCM data which is what is actually sent to the DAC.

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Old 28th September 2002, 03:51 AM   #109
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Quote:
Originally posted by Christer
I agree with you completely on this one, which leaves us
with the case "Perhaps a blue LED may improve the sound,
but it is not for the reason claimed in the article". Then we
have at least two possible ways of looking at the issue:
1) It's probably just imagination
2) Assuming it is not imagination, what could be a reasonable
explanation for the perceived improvement?
Yes. At this point it's ambiguous. Number 1 might be the case or it might not be the case. Until number 1 is eliminated as a possibility, any speculation as to physical effects is simply an academic mental exercise. Which isn't bad in and of itself.

se
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Old 28th September 2002, 03:52 AM   #110
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Default My impressions of the LED claim

Pete,

I hope to try the experiment as soon as I can locate some blue LEDS. I have to say though, that from a scientific viewpoint, there is nothing I've come across to convince me that there should be anything audible, better yet, I'm not yet convinced that the LED should alter the decoded signal in any way.

Right now, I'm reviewing Chapter 8 - The Compact Disc, in Ken Pohlmann's "Principles of Digital Audio". This is highly recommended reading for anyone who wishes to learn about the steps in encoding, decoding, servo control, error correction, etc. From what I've read so far, it seems to me that if the blue LED affected the reflected laser beam's signal (via modulation) that it would happen more likely on 1's (pit edge) where there is ~25% reflection on long pits than on 0's (~95%). The LED interference would have to confuse the photodiode that the wrong value (1 or 0 was being read). The laser's output power is ~0.5mW. I'm not sure that the LEDs optical power is in this ballpark (I need to check). It may be too small in magnitude to cause a signal transition at the photodiode via constructive/destructive interference with the reflected signal from the CD. The way you show your LED in your diagram it looks like it may be 3-4x the distance from the photodiode as the reflected laser beam is to the photodiode?

Furthermore, if the data was altered, then there would be no way to alter only the LSB. All data would have to be altered (assuming it even could be). This is what makes the theory hard to believe: CDs which utilize EFM and CIRC are extremely robust at error correction, missing 1 error out of 10 - 100 billion. According to Pohlmann, when an error is present it is flagged (if detected of course) and then linearly interpolated (most of the time - depends on the CDP). I know of some which actually mute the output. Do you see what I'm getting at? Perhaps someone will argue that linearly interpolated (which is incorrect data) data sounds better on CDs. In this case, source data from the CD is missing during decode, not restored as the LED theorists believe. So, I do not know how optical dithering can be claimed.

Anyway, I've got to more to read. No one can tell you what you hear. If it sounds better to you with the LED than that is great, and in the end that's all that matters. The cause and effect of the claim are difficult for me to understand at this point. Just as important as being able to witness improved sound is for me to try to understand this phenomenon from an scientific standpoint.

-AudioEnthusiast
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