24 bit format/bit rate and big fluctuation for Waveforms for Sound Card

[heretop]

I have two question when I use waveform with my sound card (or audio interface, Focusrite 2i4)

The "format" selection for Waveforms with the Sound Card only have 8, 16, 32 bit. I may assume this "format" means bit depth. Since majority of audio interface are 24 bit, it will be great if waveform can add 24 bit for sound card.

Second question is that there is big fluctuation when I try the bode plot. I have attached the bode plot result of some simple guitar effect circuit. When I set "format" to 16 bit, the plot start to get fluctuation around 400 Hz. For "format" as 32 bit, the whole plot have big fluctuation. May I know if this is some thing that can be improved?

 

The following system information might help us in resolving the problem:
WaveForms 3.16.3 64-bit Qt5.12.9 Windows 10 (10.0)
Connected to Sound Card  configuration 1
Qt version: 5.12.9 / 5.12.9
Screen: 1920x1040
Windows 10
Total memory: 16334 MB (unreliable)
Total virtual memory: 134217727 MB (unreliable)
Physical memory in use: 43%
Processor speed: 3600 MHz
Processor name: AMD Ryzen 7 3700X 8-Core Processor            

[attila]

Hi @heretop

The fluctuations may be caused by the audio amplifier auto gain. Try disabling it if you have such option in the sound card configuration.
Use the 32bit sampling since this fits the 24bits. The other options are just in case there is some compatibility issue.
You could try using higher Settle time in Network Options, to see if this makes any improvement. The audio stream latency may vary from systems to system.

See the related post:

 

[heretop]

2 hours ago, attila said:

You could try using higher Settle time in Network Options, to see if this makes any improvement.

This worked out great! Thank you for the great suggestion! I think the reason is due to the guitar circuit I tested is a distortion circuit. With small settle time, it will be very noisy (not sure why at high frequency only). I changed settle time from 10ms to 1s. Here is the result with "format" set to 16 bit.

However, with 32 bit "format", I still get big fluctuation even with large settle time. If adding a 24 bit option is not difficult, maybe consider add it. Thanks a lot!

FYI, I am using audio interface here, normal there is a gain knob at front which is set to fix gain. I don't think it have automatic gain, and I cannot find it in the audio interface setting.

[attila]

Hi @heretop

I've added for the next software build 24bit format option but I don't think this will solve the problem you have. In the 32bit format the 24 effective bits should fit well.

You could use the Time and FFT Views to investigate the signals like this:

[attila]

Hi @heretop

It is added to the latest beta version:
https://forum.digilentinc.com/topic/8908-waveforms-beta-download/