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How low is too low

There has been one area of discussion below that needs to be expanded upon and that is the the following question:

How low does distortion need to be before it is truly inaudible?

Naturally, this is a complicated question to answer because it seems to be for low order distortions the answer is "Not very low". For example it is widely held that 2nd order distortion is inaudible up to at least 1% with sine waves.

It also depends on which frequency band the distortion is occurring in. For example, the ear is very tolerant of distortion at bass frequencies but will be significantly less tolerant in the presence region. Tube amps generally have high distortion in the bass (due to output transformer saturation) but can measure significantly better through the whole mid to high frequency range. Is that distortion in the bass audible?

For higher order harmonics or intermodulation products it seems to be the case that we can be quite sensitive to them and these products can have a distinct audible effect on what we are hearing.

The question is how much can be present and remain inaudible?

Is it necessary to have uniformly low distortion over the whole bandwidth or is it necessary to make sure that only ear critical bands are devoid of signal damaging distortion?

Is distortion that is buried in the "noise" really inaudible? It is well known in analytical sciences that correlated signal can be extracted from noise by averaging. Take 1 scan and you see nothing but noise, take 100 scans and now you see peaks of interest. In mass spectrometry, we regularly extract peaks from the noise because the signal is correlated at that time in the chromatogram by single ion extraction.

The question is: Does the ear/brain have the ability to detect signals buried in the noise? My initial answer would be that yes it does have that ability and since distortion is most definitely correlated signal, and not random patterns like true noise, that distortion that is BELOW the noise floor could conceiveably have audible consequences in certain sensitive frequency bands.


Finally, what does this mean with regard to amplifier design? Perhaps an amp designer would be surprised to learn that what he thought was noise was really signal correlated distortion? I think people have for too long assummed they knew what the limits of hearing perception were and dismissed important features that are already in the data they have because they don't know how to mine it properly.


Any experts want to comment on these questions?

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Topic - How low is too low - morricab 08:18:12 06/15/06 (126)
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