Blackness - how quiet does it need to be?

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

Bryon, Jitter modulation produces all sorts of garbage across all frequencies raising noise floor. Normally you would not be able to hear it as a hiss because it would be covered/masked by loud signals and not audible during gaps or soft passages. Let's assume that jitter product is for instance, always -60dB down from the loudest music level. When you play softer passage jitter products are -60dB down from that being inaudible. The louder you play the more apparent it is showing as a lack of clarity (loud trumpet is not as pure as it could be etc.)

One possibility is that they suppress microphones' hiss before and after but I would agree with Al, that what you hear might be differential of high inaudible frequencies modulated on the tweeter or amplifier. These frequencies come from many sources including digital playback itself (quantization noise). New techniques of oversampling push quantization noise outside of audible range but it might come back when system is not perfectly linear and has additional noise sources (poorly filtered switching power supplies, RFI pickup etc). These high frequencies can have extremely high amplitudes. I remember that some of SACD players have bandwidth limiting switch (filter) to protect weaker tweeters from overheating just from inaudible quantization noise. Stereophile review mentioned that it was left by manufacturer to customers with warning of possible risk of turning off the filter switch. Tweeter membrane does not move much at very high inaudible frequencies but as long as it does it will modulate because its displacement vs. voltage is never perfectly linear.