Blackness - how quiet does it need to be?

Last_Lemming I'm hesitating if I should even start since Al can explain it much better and more coherent way. If he does follow his explanation.

In both cases, digital and analog, we're talking about modulation that creates new frequencies.

Two frequencies in presence of nonlinear element (nonlinear transistor, nonlinear motion of speaker's membrane) produce additional signals of frequencies that are sum and the difference of original two frequencies. You can think of it as noise since it wasn't in the music and amplifier or speaker manufactured it. Great amplifiers or speakers modulate very little but we also "learned to listen" and can detect smallest differences in clarity.

Time jitter of your transport digital signal when playing single frequency also creates two additional frequencies (sidebands), but this time they are spaced on both sides of original/root frequency by modulation frequency distance (frequency of time jitter). Al mentioned once, that this modulation frequency can be completely random at the moment (random noise affecting digital signal timing) and we call it uncorrelated or can be cause by particular frequency like noise from switching power supply - then it is correlated. Usually it is mix of both. When complex signal (music) contains a lot of frequencies there is a lot of byproducts - basically a hash proportional to amplitude of the music. When music stops hash stops. It is detectable only as a lack of clarity and as such affects pretty much everything from tonality to imaging. Jitter usually has very small amplitude and byproducts (sidebands) are very, very small but still audible since they are not harmonically related to root frequency (like in harmonic distortion) and our ears are sensitive to it.

We're dealing wit two aspects of jitter: amplitude (modulation index) and the frequency. Small modulation frequency (like 60Hz) creates sidebands near root frequency that are easily masked therefore is less dangerous but high frequencies of the jitter create byproduct far apart from the root frequency and very audible. Amplitude of the jitter affects amplitude of the byproduct up to the point where even more than two sidebands can be created. Bad CDP have often a few nanoseconds jitter amplitude while good transports perhaps one tenth of it. I shouldn't really attribute it to transport but rather to system (transport, cable, DAC, ambient noise, power noise etc.)

Al, did I miss something?

Thank you Kijanki. I do believe I get the gist in what you are saying. Since there can only be jitter when a musical signal is present, then noise can't be heard as a "hiss" per say, but as distortion on some level in the music reproduction.

Al, did I miss something?

No, I think you covered it well. The only thing I would add is to re-emphasize the point I had made that some of the spurious difference frequencies that may be created, especially as a result of intermodulation of recorded hiss or music and system-generated hiss in the speakers or other analog parts of the system, may be at frequencies that are more audible to us than the original frequencies.

With respect to the purely analog parts of the system, I'll qualify my comments by saying that I have no particular quantitative feel for how audibly significant noise intermodulation may typically be. (The significance of jitter at the point where digital is converted to analog is well established, of course). But what I am saying is that if the subjective perception of background blackness can in fact be improved by reduction of noise that is essentially inaudible when nothing is being played, the explanations that Kijanki and I have offered are the only ones that come to mind.

Best regards,
-- Al

Is the noise floor system dependent? or is it directly the sum of the noise floor of the individual components?

Thing is, when I turn on my system and no music is going through it, I can't hear anything, unless I put my ear right up to the speaker and the AC isn't running and the fan isn't on, etc. And with music on the only thing I hear is any recorded hiss that might be from the recording. So what I don’t get is when they say a piece of equipment sounds quieter, do they mean somehow that the hiss on the recording is lower? I can’t see how that would be possible...

I agree that, on the face of it, this seems impossible. But I’ve had a number of experiences that have led me to conclude otherwise.

For a long time I thought that my system was dead quiet, due to the fact that there was no audible noise floor when the system was on and no music was playing. As a result, whenever I heard hiss during playback, I believed that the hiss was in the recording.

Several months ago, I made an effort to reduce RFI/EMI in my system, which is discussed in this thread. One of the consequences of those changes was that hiss during playback was dramatically reduced. But the reduction of hiss was audible ONLY WHEN MUSIC WAS PLAYING.

From this I concluded that a significant fraction of the noise floor that I thought was IN THE RECORDING was actually IN THE SYSTEM. But the noise floor in the system was not perceptible when the system was "at idle."

I know that seems paradoxical, but that's what I experienced.

Bryon