Focusrite 18i20 (gen.2), Lavry DA10, REW interpretation

[AnalogSteph]

or a sweep from 20kHz upwards but the REW generator doesn't seem to allow me to do these.

FWIW, I could export a 20000 Hz to 96000 Hz linear sweep as WAV just fine after selecting 192 kHz as the sample rate. It just doesn't let you enter anything past fs/2, which makes sense if you think about it. For realtime generator use, you'd have to change the sample rate in settings.

Also, there's obviously other spectrogram software, but many will be familiar with Audacity already as it is a popular free general purpose audio recorder / editor that many of us will have used for something already. I did all my FM radio recording with it back in the day.
(Important: On Windows, use the WASAPI sound library to get past 16 bits per sample. You can get ASIO support if you compile a build yourself.)

 

[HenryL]

I mostly use it in stand alone mode for karaoke parties.

!

Now you could use Multitone as it will allow two devices connected to a single laptop running at different sample rates.

Mac-only here...

One way I know is using static tones. Use REW in RTA mode while playing a tone above the sample rate limit of the ADC. Run the ADC at say 48 khz, and run the DAC at 96 or 192 khz. Play tones at 25 khz or higher. You could do it every couple of khz or whatever. Record it with the ADC and you'll see as you move the tone higher it will show up at lower frequencies in the ADC. 25 khz tone will show up at 23 khz. 27khz tone will show up as a 21 khz tone when aliased. 30 khz tone will show up as an aliased 18 khz tone in the ADC. The tones will mirror around the 24 khz cut-off of the ADC. That is probably the most straightforward if tedious way with REW. You can compare the level of the aliasing vs frequency.

Right. Yes - I have been playing around with this method, using single tones from REW and also manually sweeping a bench hardware signal generator which goes up to 200kHz. It's the ease of execution / capture / comparability I liked in your set of measurements.

Thanks for your info. The spectral view in Audacity looks quite useful so I'm thinking it might well be worth the effort to get into/it anyway.

Stop press: I've just had another poke around in REW and now I DO seem to be able to set the lower/start frequency for noise and sweeps to 20kHz . I must have goofed previously - perhaps hadn't actually set the sample rate I thought I had. It doesn't seem to be possible in the general 'measurement' panel sweep range where the highest frequency allowed is 10kHz, but in the generator it all looks hunky dory now.

 

[HenryL]

FWIW, I could export a 20000 Hz to 96000 Hz linear sweep as WAV just fine after selecting 192 kHz as the sample rate. It just doesn't let you enter anything past fs/2, which makes sense if you think about it. For realtime generator use, you'd have to change the sample rate in settings.

Also, there's obviously other spectrogram software, but many will be familiar with Audacity already as it is a popular free general purpose audio recorder / editor that many of us will have used for something already. I did all my FM radio recording with it back in the day.
(Important: On Windows, use the WASAPI sound library to get past 16 bits per sample. You can get ASIO support if you compile a build yourself.)

Hi - your post just crossed in the ether with my post just now. So... Yes!
Cheers/ Henry

 

[HenryL]

Just realised that using noise for this is not a very good idea as it will be hard to identify aliased noise in with the other noise... back to sweeps.

 

[Blumlein 88]

I know Sonic Visualizer for Mac will do spectrograms. It is meant for use on music and speech. It could be used, but is clunky for this purpose versus Audacity. Audacity is pretty simple and adjustments for different views is a piece of cake if you want to bother with it. Works very nicely with Macs.