Blackness - how quiet does it need to be?

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.

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