High Frequency Tones

Special Interest Groups Audio Processing
1

Hi, I’m hoping to use Audacity for a bit of an experiment and need to generate single, high frequency tones.

The highest freq tone I’ve been able to generate is ~47kHz, based on a 96kHz project rate. Is it possible to generate even higher frequency tones, say upto to 200kHz?

I know that this is beyond audiable, but it if for a development experiment using ultrasonic/megasonic water baths?

ANy help would be greatly appreciated,

Rich

2

I think the highest sample rate that Audacity can presently use is 96 kHz, which gives you a max frequency of about 45 kHz, but it is no way representative of a sine wave. Even if Audacity used higher sample rates, your sound card would not be able to handle them. You are probably better to use an analogue circuit to drive your ultrasonic transducers.

3

Audacity 1.2.6 is limited to 100 000 Hz Project Rate and 20 000 Hz tone generation so I assume you using a 1.3.x version? I’m not sure but 1.3.5 does not seem to have any hardcoded sample rate limit, but there will be some limit as to what your sound device will accept as it will be having to resample it, and if you are using a standard sound device it would probably resample to 44 100 Hz even if it accepted the input. 1.3.5 supports Chirp and Tone generation up to half the project rate, but any tone will be distorted or flat lined close to the half project rate limit.

Gale

4

It seems to be the same in Audacity 1.3.4 (32 bit Linux) and 1.3.5 (Win XP). They will accept custom sample rates of 100kHz but not 100001Hz

5

Hi Steve

When you say they won’t accept 100001 Hz, what happens? I can generate or record at that rate, export as WAV then import back in and it shows as 100001 Hz.

Gale

6

Thanks for your comments. Much appreciated.

R

7

I did not have time for thorough test when I posted that, but in the test that I tried, I got an error message “invalid rate”.

On my Linux box at the moment, I’ll have to come back to Windows later.

Set up - Xubuntu 8.04 (32 bit) Audacity 1.3.4 Unicode (from repo). Using JACK.
“Preferences > Quality” set to 48kHz.
Create track (record or generate).
Click on track name and from the drop down menu select “Set Rate > Other”
Enter 100001.
Click “OK”.

Error message pops up - “Invalid Rate”
This was the same for Win XP with Audacity 1.3.5, and appears to be the case for any rate greater than 100kHz

However it seems that you are correct about the sample rate limit not being hard coded.

Test 2:
Set “Preferences > Quality > Default Sample Rate” to 100001.
Restart Audacity.
Generate track.
Track is created with sample rate of 100001 Hz and plays back fine.

I’m now going to try recording at 192kHz, but I’ll post this bit first in case of a major crash. (This build of Audacity is a bit temperamental on my machine).
Back in a moment…
… Yes it worked. Recorded successfully at 192 kHz :smiley:

Play back was rather jittery - a bit too much for my poor ol’ Pentium 3, but it worked.