Well, you took on the challenge and succeeded perfectly Eric! What an excellent
piece of analytic dissemination of, as I suspected, a complex subject. I very
much appreciate the time you've taken to answer this question. I'm now going
back to study this in more detail.
Cheers
Max
Sent from my iPod
On 6 Jan 2013, at 02:23, Eric Benjamin <> wrote:
>> why should a preamp be called on to amplify frequencies above 20 K if nobody
>> can hear it?
> That is an excellent question!
>
> First we must distinguish between recordings made for analysis and recordings
> made to be listened to by people. If your purpose is to assess the frequency
> range of Bat vocalizations then you had better have equipment that can record
> it. But you are not talking about that case.
>
> There are several things to remember. The first is that the frequency range
> of
> human hearing varies quite a bit between individuals. As a rough
> approximation,
> people with smaller ear geometry have a frequency range that is shifted up in
> frequency relative to the average. The second is that the threshold of
> hearing,
> the level of the quietest sounds that can be heard, is not at all flat.
> Finally, there is the important effect of auditory masking, which is probably
> most significant of all.
>
> It's worth taking a look at a typical threshold graph:
>
> http://en.wikipedia.org/wiki/Equal-loudness_contour
>
> This data is from an ISO standard, ISO 226:2003. It's a bit of a moving
> target
> because different labs in different places get different results, and in any
> case this curve is meant to represent an average result. But an important
> thing
> to note is that the thresholds get worse (higher) at low frequencies and at
> high
> frequencies. Compared to earlier editions of the standard the present one
> doesn't have data for frequencies above 12.5 kHz. This is because there is
> too
> much variation for them to come up with a representative figure. The dotted
> lines are an extrapolation.
>
> You can see this a bit better in Figure 1 of this paper by the folks at
> Etymotic Research:
> http://www.etymoticresearch.com/publications/erl-0096-1997.pdf
>
> You will see that they show the threshold going pretty much straight up as
> the
> frequency approaches 20 kHz. Hearing pretty much stops working at some very
> high frequency. The frequency at which this occurs does vary from
> individual
> to individual. In "Recommended High-Frequency Audiometric Threshold
> Levels (8000-18 000 Hz) ", JASA Vol52, No. 2, The authors obtained a mean
> threshold value of 59 dB at 18 kHz. They didn't obtain data for higher
> frequencies.
>
> At low frequencies the behavior is completely different. The threshold keeps
> rising as the frequency decreases but there is no clear cutoff. So basically
> the 20 Hz to 20 kHz frequency range is a misnomer. If one were to define the
> frequency range of human hearing as the range which we can hear at a level of
> 60
> dB SPL then, using the data from the above sources, that range would be about
> 30
> Hz to 18 kHz.
>
> Finally, there is the effect of masking. If the sound being recorded is
> complex
> and has lots of overtones then the louder, lower frequency sounds "mask" our
> ability to hear the higher frequency sounds. This is why we can't hear the
> phone ringing while we're in the shower; the noise of the shower produces a
> lot
> of masking.
>
> Backing away from all of this analysis for a bit, it's really easy to make
> preamplifiers that amplify 20 kHz, or 40 kHz, or 200 kHz. But it's very
> difficult to make microphones that do that. And even if a microphone is flat
> up
> to 20 kHz on the axis of the microphone, it almost certainly has a very
> narrow
> polar pattern at those high frequencies. So it's quite conceivable that a
> microphone that is "flat" to 20 kHz actually transmits very little sound from
> a
> subject that is off axis, effectively making a 10 kHz or 5 kHz microphone.
>
> Eric Benjamin
>
>
>
> ________________________________
> From: Max <>
> To:
> Sent: Sat, January 5, 2013 4:47:33 PM
> Subject: [Nature Recordists] Re: Olympus LS-14 initial thoughts
>
>
> This post of Greg's brings up an interesting question for a hearing impaired
> person like myself. Even using both my hearing aids, I don't hear anything
> above
> 9K. Even people who hear well, as I understand it, rarely hear 20K. So, the
> question is, why should a preamp be called on to amplify frequencies above 20
> K
> if nobody can hear it? I frequently see references to magnitudes above 20K;
> I'm
> guessing this is purely techno babble. I realise of course that these
> frequencies are real, but humans can't hear them any more than they can see
> in
> the infra red.
> I feel sure that there's a perfectly logical, if complex reason for this, and
> perhaps it's not easy to explain simply, but if it is I'd be interested to
> hear
> it.
> Cheers
> Max
>
> --- In Gregory O'Drobinak wrote:
>
>> "a preamp that may be called on to amplify frequencies above 20 KHz."
>> Greg O'Drobinak
>
>
>
>
>
>
>
> ------------------------------------
>
> "While a picture is worth a thousand words, a
> sound is worth a thousand pictures." R. Murray Schafer via Bernie Krause.
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