| Re: Is 16/44 high enough? [message #60497 is a reply to message #60493] |
Thu, 30 July 2009 09:46  |
SASAudioLabs
Messages: 17
Registered: May 2009
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Chancellor |
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| Wayne Parham wrote on Wed, 29 July 2009 15:18 |
I wonder if it's the untrasonics or possibly the waveshape or distortion. In a way, these are all ways of saying the same thing because harmonics would be shifted up out of the (traditionally recognized 20-20kHz) passband and waveshape modifiers can be expressed as (Fourier series) harmonics.
On the other hand, it could be that the real issue is something like non-linearity, where it may be that the audible thing isn't so much the high frequency harmonics as it is the non-linearity itself - the harmonics are just one way of seeing the non-linearity, a side effect, if you will.
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I can see other possibilities as well, such as overall rise time changes? Whatever it is, or combination you and I have pointed out, I would rather be on the safe side.
Here is some more information from Dr. Kunchur's papers.
"The temporal resolution and high-frequency audibility
of human hearing are complex issues of both fundamental
and practical significance. While the single-tone highfrequency
threshold fmax for airborne stimuli is around 18
kHz in individuals with good hearing (Pumphrey, 1950;
Hall, 2002), a much higher bandwidth and temporal acuity
can play a role in the complete perception of the timbre
of sound.
Neural processing beyond the cochlea can permit
extraction of temporal information at time scales τ
shorter than the 1/2πfmax=9 μs that would be nominally
expected for a linear system. In binaural localization by interaural
time difference, it is well known that differences in
arrival times of order 10 μs are distinguishable (Henning,
1974; Nordmark, 1976). Monoaural experiments involving
iterated ripple noise (IRN) and inter-pulse gaps have
shown similar thresholds in temporal resolution (Krumbholz,
2003; Leshowitz, 1971).
A similar sensitivity for temporal
fine structure can be inferred from the discriminability
of the virtual pitch of complex tones (Moore et al., 2006;
Gockel et al., 2006).
It also appears that the cochlea may
sense ultrasonic stimulation if the latter manages to reach
the cochlea in sufficient intensity, both when presented
through the air (Henry and Fast, 1984; Ashihara et al.,
2006) but especially when presented through bone conduction
(Corso, 1963; Deatherage et al., 1954; Lenhardt et al.,
1991; Lenhardt, 1998).
It has also been conjectured that
such high level ultrasound may possibly change the perception
of timbre when superimposed on audible harmonics
(Oohashi et al., 1991; Yoshikawa et al., 1995). Additionally,
restricting the bandwidth by low-pass filtering necessarily
attenuates all frequencies to some extent, and hence
spectral amplitude changes can never be avoided absolutely
(even when 1/τ>>fmax); how those amplitude changes affect
timbre will depend on their magnitudes relative to the
relevant just noticeable differences. For these reasons it can
be expected that limiting the bandwidth of an audio signal
by low-pass filtering may produce an audible change, even
when the high-frequency cutoff (or equivalently [2πτ]−1) is
well above fmax. The present work experimentally confirms
this to be true, and at intensity levels and time constants
much lower than suspected possible before."
Of all the possibilities both you, me, Dr. Kunchur have presented, I want to play it safe and go beyond the bare minimum.
Take care and thanks. 
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