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Old 11th April 2012, 05:20 PM   #31
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Originally Posted by SoNic_real_one View Post
That's 4 seconds? You say that the DAC anticipates that the music will start playing in the next two seconds and raises the noise? That implies that it has some kind of time-delay line, buffer memory. Or has some other kind of time-travel device inside.
I took this to mean that the recording has started playing back, but the performance hasn't started so we're listening to the acoustic that the performance is about to take place in.

Some people will apply proper silence in periods like this whereas others will simply let us listen to the acoustic.

Certainly if with one CD this period is noisy and on another it is not, it implies that the noise is actually on the CD so we're not actually listening to zeros but a signal of some sort.
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Old 11th April 2012, 05:21 PM   #32
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Nope, you'll need to read the thread a bit more carefully. This is just an experiment to demonstrate that 5th's understanding of masking is rather too simplistic. It has no direct connection with any DAC.
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Old 11th April 2012, 05:29 PM   #33
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Here is an example of just that happening. This is the opening of of Strauss' 4 last songs as sung by Renee Fleming.

Click the image to open in full size.

This is with 57dB of gain applied. The start is true digital silence and what follows it is the noise when the faders go up, the performance is still yet to begin.

If a recording didn't have true silence put in at the start you'd get noise playing as soon as the track starts playing.
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Old 11th April 2012, 05:32 PM   #34
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So now I've given you my data set are you going to respond to my earlier question?
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Old 11th April 2012, 06:24 PM   #35
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And what question would that be? Your dataset, if by which you are meaning the audacity screen shot, looks almost identical to mine. Digital silence followed by the faders going up = recorded noise. I don't see what it is you're trying to ask.
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Old 11th April 2012, 06:27 PM   #36
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Post #23, my third paragraph.
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Old 11th April 2012, 08:26 PM   #37
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I have answered this a few times over already I feel. Yes, the noise floor on those CDs is only ~60dB below maximum amplitude.

If you are hearing noise played through the system with some CDs and then not with others then you have to think why. Now it stands to reason that the CDs that present you with no noise will have true digital zero in the data stream. Those that have noise will have something else. I suggest that you record true digital zero onto a CD and see what happens when you play it back. You could also record several tracks with noise recorded at different levels. , -90dB, -80, -70 etc and see what happens, and then also listen for when the noise becomes audible.

There could be a couple of things perhaps occurring here. One is that the DAC, when fed with digital zeros, actually holds the output in a muted state so that any noise the output stage of the DAC might intrinsically produce is not heard. However when fed with something less then zero, the output is engaged and the true noise floor is revealed. Here the encoded noise is below audibility, but the DACs own intrinsic noise dominates and you hear it.

If you wanted to, you could also record 20kHz sine waves onto the CD, or a sine wave of an appropriately high frequency so that you cannot hear them. The sines could be at 0dBfs -10, -20....then if you are unable to hear the tone, if the reproduction of it by the DAC is going to produce noise, then you should be able to hear the noise.
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Old 11th April 2012, 11:12 PM   #38
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Quote:
Originally Posted by 5th element View Post
Yes, the noise floor on those CDs is only ~60dB below maximum amplitude.
Please explain the steps you took to determine this from the waveform I posted?
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Old 12th April 2012, 12:04 AM   #39
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ICertainly if with one CD this period is noisy and on another it is not, it implies that the noise is actually on the CD so we're not actually listening to zeros but a signal of some sort.
Exactly! The DAC doesn't know when the music is about to start, but the mixing engineer knows. He raises the faders up right before that and we see the analog noise.
The 2 seconds "before" noise modulation is not happening in the DAC, is in the mixing console. DAC cannot hold that much data to anticipate for 2 seconds.
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Originally Posted by 5th element View Post
One is that the DAC, when fed with digital zeros, actually holds the output in a muted state so that any noise the output stage of the DAC might intrinsically produce is not heard. However when fed with something less then zero, the output is engaged and the true noise floor is revealed. Here the encoded noise is below audibility, but the DACs own intrinsic noise dominates and you hear it.
I think all the S-D DAC's do that - it is called "zero detect mute".

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Old 12th April 2012, 04:41 PM   #40
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Please explain the steps you took to determine this from the waveform I posted?
Well determining the exact level of the noise it does not, but it does put you in the ball park range. I posted my own version of what you posted in post 33. The signal has been amplified by 57dB. The start shows no change as that's true digital zero, but then the noise gets boosted right up to 0dBfs as soon as the faders are brought up. The real noise floor of that environment is clearly around -60dB.

Of the wave-form you posted, you never mentioned if it is one of the CDs that hits you with noise as soon as the data stream starts. Regardless of if it does or doesn't, if your system really is playing back noise with some CDs and not with others, then you need to investigate exactly why this is so.
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