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Jeff Wong
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Why the "bits is bits" argument may not hold water

I'm sharing a letter from a computer programmer friend who felt he understood why the "bits is bits" argument doesn't actually hold true:

I guess the question of whether CD audio reproduction is analog or digital comes down to your definition of digital. What does it mean to be digital? Wikipedia has this definition:

Monty
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Re: Why the "bits is bits" argument may not hold water

I can see where your friend is coming from. But, I kinda think he is stating the obvious or I'm missing his point, which may very well be the case.

At some point between storing information in a digital format and the eventual playback something has to convert the information into a usable electrical signal.

I guess he is suggesting that a purely digital format would not involve any conversion. Am I missing something?

Jeff Wong
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Re: Why the "bits is bits" argument may not hold water

I suspect what he may be getting at is that in a computer, 0s & 1s always remain hard digital, black and white, and unchanging... but, that with the EMF code in a CD the voltage level changes representing the transitions are more instructions than data, and may be subject to variations, which could explain why various tweaks might alter CD sound when we all "know" they shouldn't.

Jim Tavegia
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Re: Why the "bits is bits" argument may not hold water

http://www.stereophile.com/features/827/

Great Robert Harley article.

Computer recording became more reliable when CDR burners added buffer underrun protection, reclocking the data stream on demand. There is so much more going on within the 9 bit lengths, including bit depth, that makes the 16 bit, perfect sound forever, a remarkable achievement. And, just because you recorded it well, as Roger Nichols, Steely Dan's engineer found out, disc pressing has its own potential problems. Remember, the sound of the DCS stack was "improved" by adding the external Verona Clock. That really make me wonder how much I have been missing. A LOT!

I am convinced that just like you can't hear all vinyl has with a Technics $120 TT and that swell Radio Shack phono stage, you have left too much information behind. In digital, a great cd player is the difference between the Hubble Telescope and Lens Crafters. If you want to see and hear "deeper" you must get serious. The reality is it is amazing that a $39 DVD players does what is does at all. There are some really, really bright folks out there.

Those engineers that have taken us this far were basically given a system with criteria that a certain Beethoven Symphony must fit on one side...now that we've tied one hand behind your back, get to work. There is a reason the Ayre C7-XE costs and is worth $3 grand and JA chose to own a C5-XE. It is the same reason Michael Fremmer bought the Continuum Caliburn. It was about the experience and the value...to them.

Since the originators heard sonic improvement with sample rates out to 500khz it is no wonder DSD is remarkable, irregardless of the marketing failures. It is much more about sampling rates than bit rates. Just as 30ips was better than 15 and 7 1/2 ips in tape formats.

WE ARE IN THE MOST AMAZING TIME OF AUDIO REPRODUCTION AND WE STILL COMPLAIN AND WANT MORE. Go figure.

While writing this I am listening to a jazz stream from WDCB outside Chicago. Talk about trickle-down theory.

dcrowe
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Re: Why the "bits is bits" argument may not hold water

Jeff, the letter is not entirely clear to me, but it appears to me to state that errors occur in digital systems, and at the analog interfaces. These are true statements. Every system has limitations. "Digital" systems still have some advantages after their imperfections are taken into account. My philosophy is to just listen and/or measure the end-to-end system performance and decide what you like best!

Jeff Wong
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Re: Why the "bits is bits" argument may not hold water

My programmer pal didn't feel I distilled things quite right and sent this clarification:

To clarify my previous statement, I guess the best way to describe CD audio is to say that it is half digital, half analog. The signal levels are digital, but the signal timing is analog. The timing signal start at the laser pickup and passed down to the DAC, being thrown off a bit here and there along the way. And that analog signal, along with anything that throws it off, ends up driving the generation of the final audio signals. I just have a hard time calling it

Monty
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Re: Why the "bits is bits" argument may not hold water

Now it all makes sense.

I never bought the "bits is bits" arguement in the first place. No sooner did CD players hit the streets than people started tweaking them with different opamps, damping and reclocking to turn the average into giant killers.

dcrowe
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Re: Why the "bits is bits" argument may not hold water


Quote:

...he was able to see the distinction between how bits are handled in computer function and in CD playback.

Quite true. Computers are not perfectly digital either, but in different ways.

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Re: Why the "bits is bits" argument may not hold water

This is fascinating. I'm a bit of a Luddite when it comes to understanding some things, but this really helped!

So, simplistically speaking, what we need is a "reader" to get the bits from the CD, a buffer to get all the bits together in one place, and then a DA converter that uses the buffered data "at its leisure" to decide how to create the proper analog signal.

That doesn't sound all that hard to do, he said naively.

PhilNYC
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Re: Why the "bits is bits" argument may not hold water


Quote:

So, simplistically speaking, what we need is a "reader" to get the bits from the CD, a buffer to get all the bits together in one place, and then a DA converter that uses the buffered data "at its leisure" to decide how to create the proper analog signal.

Theoretically, this is correct. However, things that must be taken into account include:

-When reading the data out of the buffer, it must be done with an extremely precise clock; otherwise an imprecise clock will add jitter to the data stream, and the buffering will have been pointless.

-The clock used to read the data out of the buffer must be sync'd to the clock used by the actual DAC chip in order to keep jitter out...or it must be the same clock.

-The device that recreates the digital signal must also be extremely accurate; each bit or set of bits must be as close to a perfect square wave as possible.

Mono
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Re: Why the "bits is bits" argument may not hold water


Quote:

To clarify my previous statement, I guess the best way to describe CD audio is to say that it is half digital, half analog. The signal levels are digital, but the signal timing is analog.

Just curious... how does this differ from playing back audio from an application like WaveLab with the audio on a hard drive? How is the signal timing done?

cyclebrain
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Re: Why the "bits is bits" argument may not hold water
Quote:

The signal levels are digital, but the signal timing is analog.

Actually both the timing and levels are analog. They both have imperfect variations in their timing and levels that fit the analog definition.
It's the tolerance range of the timing and levels defined by the specification that converts the analog signal to digital data.

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