14 Replies Latest reply on Sep 26, 2014 7:57 AM by rrich

    Recording up to 192kHz?

    macaodha

      Hi there,

       

      I'm interested in investigating this board for creating ultrasonic recordings of animal noises. Some of these animals generate calls that are of a high frequency. I was wondering if anyone knows if ill be able to record audio up to 192kHz?

       

      Thanks

        • Re: Recording up to 192kHz?
          ragnar.jensen

          The maximum theoretical audio frequency is half the sampling  frequency. Nyquist–Shannon sampling theorem - Wikipedia, the free encyclopedia

          Thus, if the hardware were perfect, the max audio frequency you could record would be 96 kHz.

          But, as we all know, hardware is never perfect.

           

          I did a quick test by feeding white noise at a 192 kHz sample rate into the Line In of the Wolfson card and recorded it.
          Using Audacity's "Plot Spectrum" I got a chart showing the audio frequency response of what was recorded:

          WAC_96kHz_test_SpAn.png

           

           

          I actually did not think it would go so high.

          I have seen (and heard) several high-end Hi-Fi systems that roll off sharply when they get above 20 kHz (yes, I know that it can be done on purpose.)

           

          What are the frequencies you're interested in?

          --

          Ragnar

            • Re: Recording up to 192kHz?
              macaodha

              Hi Ragnar,

               

              Thanks for your very detailed reply. That was really helpful.

               

              I'm interest in recording bats which emit calls from around 12-160 kHz. If I could record calls up to 96kHz I would be happy. Do you have any experience using different ultra sonic mics with the Wolfson card.

                • Re: Recording up to 192kHz?
                  ragnar.jensen

                  Alas, I have no experience with such microphones. My interest in high-frequency audio is in analyzing the output from FM stereo transmitters. I'm happy if I can record up to 77 kHz.

                   

                  The card starts to struggle above 94 kHz, the sensitivity curve wobbles up and down quite bit up there. Anyway, up to 94 kHz should be doable if the rest of your gear is up to it. If you record at 24 bit depth, you should be able to compensate in software for the reduced sensitivity at the higher frequencies.

                  --

                  Ragnar

                  • Re: Recording up to 192kHz?
                    rrich

                    macaodha wrote:

                     

                    I'm interest in recording bats which emit calls from around 12-160 kHz. If I could record calls up to 96kHz I would be happy. Do you have any experience using different ultra sonic mics with the Wolfson card.

                     

                    The Panasonic WM61a appears to have very good high frequency response and is available relatively inexpensively through ebay (they have been discontinued).  There are some MEMS microphones that also have very good high frequency response from Knowles (their Si-Sonic line) as well.  Commercial ultrasonic microphones seem to all be priced quite high for the hobbyist.

                     

                    Edit: Duh, didn't even look at the audio card specs...it's got two mics on the board.  Ragnar, were these the mics you were using with your frequency response test?

                    • Re: Recording up to 192kHz?
                      hystrix

                      If you are still interested, I am recording bats with the Wolfson card and home-made ultrasound mic plugged into the headphone socket.  The mic is an electret type. Choose one with a good frequency response - the data sheet for the one I used gives an upper limit of something like 20kHz, but seems to be good enough for bats....:

                       

                      sonogram.JPG

                       

                      sonogram2.JPG

                       

                      I'm recording at 192kHz: arecord -Dhw:0 -r 192000 -c 2 -f S32_LE -d 15 /home/pi/sounds/bat.wav

                       

                      I also found that the onboard mics worked OK, but not as good as the electret mic.