difference tones question etc.

If you put frequencies of 30 kHz and 31 kHz into a recording system
that has an upper limit of say 20 kHz, does anything come out? Assume
both frequencies go into the same mike to save complications.

So far as I understand it, there is no actual 1kHz power in the input,
and in general audible difference tones only arise from nonlinearities
in the ear.

Another question is whether 'inaudible' frequencies affect timbre - if
the fundamental is at 10kHz, and your limit is below 20k, does it make
any difference to vary the harmonic content?

~~~T~~~

--- In tuning@yahoogroups.com, "Tom Dent" <stringph@...> wrote:
>
>
> If you put frequencies of 30 kHz and 31 kHz into a recording system
> that has an upper limit of say 20 kHz, does anything come out? Assume
> both frequencies go into the same mike to save complications.
>
> So far as I understand it, there is no actual 1kHz power in the input,
> and in general audible difference tones only arise from nonlinearities
> in the ear.
>
> Another question is whether 'inaudible' frequencies affect timbre - if
> the fundamental is at 10kHz, and your limit is below 20k, does it make
> any difference to vary the harmonic content?
>
> ~~~T~~~
>

Actually, difference tones occuring due to nonlinearities is the fact.
"In the ear" is just one example. Ever played two notes through a
loud, distorted guitar amp? Then compared to individually?

The significance is that difference tones are not just neurological,
the same nonlinearities of difference tones from audible notes
may apply EVEN WITHIN THE EAR to ultrasonic tones as well.
(note the "may..." I am not an expert to be referenced as
proof of anything).

--- In tuning@yahoogroups.com, "Tom Dent" <stringph@...> wrote:
>
>
> If you put frequencies of 30 kHz and 31 kHz into a recording system
> that has an upper limit of say 20 kHz, does anything come out? Assume
> both frequencies go into the same mike to save complications.
>
> So far as I understand it, there is no actual 1kHz power in the input,
> and in general audible difference tones only arise from nonlinearities
> in the ear.
>
> Another question is whether 'inaudible' frequencies affect timbre - if
> the fundamental is at 10kHz, and your limit is below 20k, does it make
> any difference to vary the harmonic content?
>
> ~~~T~~~
>

To answer more specifically, if two frequencies of 30 and 31 hit a
microphone, they will cause a difference tone due to nonlinearities
of the microphone. At least I'm pretty sure they will, if I understand this
right.

Full point being: recording this with a mic live where both 30 and 31
are in the room together, the nonlinearity will happen at the mic and
record 1K energy.

If recording with a system limited at 20K, this will happen still.

But recording separately will get two recordings of nothing, which
will sum to nothing.

But a system limited at 40K will have THE SAME audible 1K whether
recording both sounds live or overdubbed. Therefore, 40K recording
adds to 20K recording even below the 20K level. See?