Blackness - how quiet does it need to be?

The OP's question, regarding how noise that is not audible beyond a very short distance from the speaker when no music is playing might have audible significance, is an excellent one, that I've pondered myself at times.

I think that Kijanki's answers are on the mark.

In the digital domain, the explanation is easy, namely jitter effects, as he indicated.

In the analog domain, it is not that clear, but the one explanation that occurs to me relates to intermodulation effects, as he also indicated. The ear is much more sensitive to some frequencies than to others, as can be seen in the figure in this Wikipedia writeup on the Fletcher-Munson Effect. Non-linearities in the speakers, and perhaps also in the electronic components that are in the analog signal path, will result to some degree in intermodulation effects, producing (at very low but conceivably significant levels) new frequencies corresponding to the sum and difference between all of the frequency components that are present. Hiss typically contains a mix of essentially all frequencies within some broad range, especially in the upper treble region (and beyond, at ultrasonic frequencies that are inaudible in themselves). Perhaps intermodulation of some of the frequency components of the music (and perhaps also frequency components of recorded noise, tape hiss, and/or LP surface noise) with those upper treble and ultrasonic system noise components results in difference frequencies in the lower treble or mid-range regions, where the ear is more sensitive.

That's my speculation, anyway, elaborating on what IMO were excellent answers by Kijanki.

Regards,
-- Al

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

Vance (Vhiner), thanks for your comment. This has indeed been an excellent discussion.

08-09-12: Nick_sr
Is the noise floor system dependent? or is it directly the sum of the noise floor of the individual components?

Nick, yes, there is a good deal of system dependency involved.

With respect to the analog parts of the signal path, the audible significance that ultimately results from noise that is generated, introduced, or picked up at any point in the signal path will vary depending on the relation between the signal as it exists at that point and that noise, especially the ratio of their amplitudes. Which in turn will depend on the gains, sensitivities, and output levels of other components in the signal path.

With respect to digital parts of the signal path, many variables and interactions that are relevant to noise sensitivity and its ultimate effects on jitter come into play between the transport or other source component, the component in which D/A conversion is performed, and the cable connecting them. Obviously the jitter rejection characteristics of the DAC are one. Also, the risetime and falltime of the output signal from the transport, which are parameters that are usually unspecified, will significantly affect the consequences resulting from noise that is present at the interface between the transport and DAC. Impedance mismatches between the two components and the interconnect cable will inevitably be present to at least some small degree, and might affect the consequences of noise at that interface, if the mismatches result in distortion of critical parts of the waveform. Also, noise that may be introduced by ground loop effects will be affected by the interaction of various technical characteristics of both components.

Best regards,
-- Al