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External sound card for THD measurements

I'm shopping for an external sound card to use for THD measurements.
Also if anyone has experience measuring THD I would appreciate any input. Open to all suggestions. Thanks guys.


  • Motu M2 .

    I'm not deaf, I'm just not listening.
  • edited January 1

    Actually I’d you can swing it, it looks like the Motu M4 has a better ADC.

    RME ADI-2 Pro is at the top of the list at ASR, it has quite a price tag too though.

    If your just looking to analyze distortion of loudspeakers, most any USB interface is good enough, but a quality mic is important too. If you’re looking to analyze distortion of other electronics, you’ll be limited performance of your own DAC and ADC , as the measured distortion will be that of the weakest link from output to input.

    I'm not deaf, I'm just not listening.
  • I can measure speakers with Omni mic (not perfect I know). I'm looking to get more accurate measurements on gear and even individuals components like caps,resistors and op amps.
    I have also been considering getting a scope and a function generator. I do have access to a few at work but set up and tear down can be such a pita. If a audio interface can get the job done then that would be a much simpler solution.

  • edited January 1

    For audio frequencies any PC soundcard, USB audio interface or even a cellphone with a headphone jack can be a basic function generator (there's an app for that). For audio stuff a soundcard with a resistor divider probe like what is in my measurement jig can function as a scope and spectrum analyzer for many tasks, but a real scope is going to be a lot more versatile if you're really wanting to do some electronic troubleshooting and circuit design. Luckily they can be had quite cheaply these days. A basic scope isn't really going to be doing any (T)HD type of analysis though. For soundcards, like I said, distortion measurement is only as good as the weakest link, so I've suggested some options that are known to perform well.

    I'm not deaf, I'm just not listening.
  • I was unaware of the Motu products before. Very nice looking products and a good value when you look at the specs.
    I will have to look into the measurement process a bit more. Do you have a link to your rig?
    Thanks for the help.

  • Just follow 4thtry's 2 channel measurement system thread. He's in the process of replicating the same jig, and my schematic is posted in there.

    That jig is purpose built for testing loudspeakers, but can also be used for analyzing frequency response of most audio electronics as well, and distortion as well given the limitations I've mentioned. Active filters, passive filters, DSP transfer function, all can be measured with great accuracy. If I were to purpose build something for in-circuit analysis though I would do it a bit differently, probably just build "cable probes" rather than a jig in a box, and include a switch for a couple different levels of attenuation, and probably some voltage protection too so I don't break my sound device if I connect it to too high of a voltage.

    I'm not deaf, I'm just not listening.
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