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Old 19th July 2004, 06:29 PM   #71
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The word varies in that it changes from sample to sample. Unless you listen to Glass or Stockhausen.
Can we now kill the utterly pointless continuation of this thread? You are going do thing your way, Jobstens is going to things his way and I'm going to do things the right way, so nothing is going to change. Now, I shall attempt to follow my own advice.
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Old 25th July 2004, 09:55 PM   #72
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rfbrw and jbokelman

Y' all have made your point to me in this thread. I just need to put a pen to paper now. I was just reading over some simular stuff on 2's comp coding in an old analog-digital coversion note book back from the 80's, so I not dismissing what you've both has stated.

My head can be fairly hard.
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Old 26th July 2004, 08:50 AM   #73
adx is offline adx  New Zealand
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Wow what a hugely confusing thread! Not the subject matter, but who is saying what and why. I think it's best that I remain at least partially confused.

My thoughs on the matter of inverting digital data:

I often think of digital zero as the halfway point between the 2 middle samples - in 2's complement this is -0.5 (I think). In a properly dithered PCM signal, the DC point in 2s complement is also -0.5. In offset binary it is 32767.5 for 16 bits. (Think about a 1 bit DAC if you don't believe me.)

So inverting the bits is the correct way of inverting the signal (without introducing a DC offset). If the signal is recorded so that binary zero corresponds to voltage zero, then it has a built in +0.5 LSB offset. Inverting the data bits on it will then introduce a 1 LSB offset. Evidently some people do care.

But it can be a Bad Thing: Inverting the bits and adding 1 (subtracting? never can remember) has the nasty side effect that full scale overflows, giving nasty distortion. Many CDs are recorded with a significant amount of clipping, and in some this is maxed out + and - fullscale signals. In 2s complement, the full scale swings are unequal: -32768 to +32767.

On a slightly related subject, CD players mute at binary zero, which is a slight offset. Or maybe they compensate. DKDC.

Conclusion: Audio signals "should" be recorded and treated so that zero is halfway between 0000... and 1111.... (or 0111 and 1000 in offset binary).

There is something to be said for vinyl.

(edits: typos)
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Old 26th July 2004, 01:58 PM   #74
gmarsh is offline gmarsh  Canada
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Though it's been said already, simply inverting the I2S data line for 16 bit I2S data will transform -32768->0->32767 to 32767->1->-32768. Inverted phase, DC offset of 1LSB.. For 24 bit DACs it's the same thing but the 1LSB error probably isn't even measurable. I wouldn't be too concerned about it.

I have no idea if the mod produces any audible effect or not, but I'd imagine it's the same as reversing the +/- on your speakers.
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