Blackness - how quiet does it need to be?

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.

Guys,

I'm a long time audiophile and I just wanna say that this has been one of the most informative, easy-to-read threads about "noise" as it pertains to equipment that I've ever read. Kudo's to all and thanks for taking the time

Vance

There's one more thing I'd like to add to this and it's from another thread about believing in magic. It's in the last paragraph before the last line.
http://www.physicsforums.com/archive/index.php/t-122756.html

This lead me to ask if you hear this hiss with all recordings or with just some.
I knew that some recordings have a lot of processing but I never knew that lots of recordings have white noise pumped into them. You could very well be hearing negative artifacts from the recording process as well as the jitter errors mentioned above.

All the best,
Nonoise

It may have been covered to some degree by your discussion in the
context of digital, but to me, i think it goes way beyond hiss- it is the
resolving power of the system to pluck out the nuances of the music or
voice against the background at low levels. The more 'absent' the
background, like ambient noise, the better you can hear all the little things
that are going on in the recording. (rough analogy would be trying to hear a
conversation in a noisy room, compared to quiet space). i think there is a
tendency to
turn up the volume to get more reality, and while that makes it 'louder,' it
doesn't make it more real sounding- in fact, sometimes the opposite
happens; the natural volume of the recorded performance is exceeded and
rather than sounding more lifelike, the system sounds like a sound
reproduction system. So, one 'test' (not really a test in the scientific sense,
but sort of a 'by thumb' way of getting the sense of a system) is how well it
resolves stuff at low volume. Not 'detail' per se, but the nuances, the
shading, the dynamics (differences between loud and soft) at a lower
overall volume level. if a system can do that well, i think it has a low 'noise
floor' in the sense that the music is presented with less ambient junk
around it and
stands out more clearly against the so-called 'black background.'
The point above about the 'natural volume' is a little different, and is just
that there seems to be a db level on playback where the recording just
sounds right, given how it was made, your system, room acoustics, the
type of music, etc. Kinda 'clicks in' just like getting the VTA on a tonearm
has a 'right spot' for a particular record.
And while the recording itself may have nothing to do with the noise floor of
the system, a system with a lower noise floor should be able to benefit
more from a good recording, if the above makes any sense.
my 2 centavos.

"I knew that some recordings have a lot of processing but I never knew that lots of recordings have white noise pumped into them."

The hiss I'm talking about is only on a few select cd recordings of older music. Like my Miles Davis, Kind of Blue HDCD. Most music sounds pretty quiet.