As a bit of background, there was a big news item recently about a
device sold in the the UK which emits high pitched whining noises to
keep teenagers out of stores, on the assumption that they don't buy
things and generally just cause trouble.
This idea was then apparently used to create a cell phone ringtone
only audible to teenagers, or at least people under 30. This sparked
a bunch more news stories, and a fair amount of interest in people
trying to determine the limits of their hearing range. So that's why
the issue came up. I'm pretty sure my soundcard is capable of at
least 44.1kHz, and I don't know that i can hear above 22.05, so
aliasing isn't really a concern.
On 8/5/06, gale@... <gale@...> wrote:
> | From "Andrew Cosand" <andrew.cosand@...>
> | Wed, 19 Jul 2006 16:03:21 -0700
> | Using Audacity 1.2.4 on windows XP, it seems that if I select
> | Generate>Tone and pick a frequency above 20,000 Hz, it defaults back
> | to 20000.00. I presume that the tone is also defaulting to 20kHz, but
> | I'm not sure.
> Further to our earlier reply, yes the tone generator is limited to
> generating tones between 1 Hz (most speakers won't reproduce below
> 20 Hz) and 20 kHz (which is almost at the upper hearing range for young
> adults, and beyond that of the average middle-aged adult).
> Note that aside from the limitation in the tone generator, to generate
> tones of a particular frequency, you need on the Quality tab of
> Audacity Preferences to set the Default Sample Rate to at least double
> the value of the tone frequency you want to generate, This is because
> a given sample rate can only carry a frequency of up to half that value.
> If you generate a tone of 20 000 Hz in a track with a sample rate below
> 40 000 Hz, the tone produced will actually be far lower: e.g. a 20 000 Hz
> tone generated in a track with a sample rate of 22 050 Hz will only be
> of 2 kHz.
> If for example you want to generate tones above 20 000 Hz in Audacity,
> create a 20 000 Hz tone in a track with a sample rate of at least
> 44 100 Hz then click on the track dropdown menu (above the mute/solo
> buttons) > Set Rate > Other and enter in the box a higher sample rate
> than the current one. Note this also shortens the track, so when
> generating the tone, create a greater length than you need to
> Gale Andrews
> Outbound message virus free.
> Tested on: 8/5/2006 5:33:55 PM
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