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SOMO II sound volume wobbling

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  • SOMO II sound volume wobbling

    Hello All
    I'm working with a somo II module and an arduino board.
    I've built my own library and the datasheet is very light. some command execution time would be welcome because some delays must be added between commands to have a good working system (the busy line works only when playing) and I had to use a scope with module answer enabled to understand the problem ("CRC error" from the module because two commands were received too fast like "continuous play" + "folder and track" )
    but my problem is not there.
    I have some troubles with the files playback volume.
    I have tried to use wav files, mp3 files, different bitrates (11K up to 48KHz), mono, stereo, different bit dephts (8 to 16bits) but I have the same trouble.
    some files are well played with the same volume and the volume change for some others.
    the files are ok and tested on the computer before to copy them on the µSD card
    the board:

    the board is powered at [email protected] with 1K on Tx/Rx lines with the arduino nano 5v board. the speaker is 8 ohms one and it's not the thermal protection of the audio amp.
    here is a link on a video.carefully listen the messages at 14, 55 seconds and 1 min 12s.
    the volume is variying but not for the other files. this file is playing well on my computer.
    there's some bug?
    Last edited by Genesis; 3 March 2015, 06:37 PM.

  • #2
    Hello Genesis,

    Welcome to the forum.

    These files you have. Have you normalised the MP3 files so the volumes are actually the same, or are you only basing it on them sounding OK on your PC?
    There are many pieces of software available which allow you to normalise a bunch of MP3 files so their output volume is the same. I suggest you try this.

    We are not aware of any volume issues with the SOMO-II at all, so I can only assume the files you are using have volume differences which you may not be able to detect on your PC, but are causing a problem on the SOMO-II.

    Please try and normalise your files so they are all the same output volume and try again.

    Could you possibly attach one of the files you are having problems with so we can try it on the SOMO-II? Maybe the format is not 100% compatible for some reason, and you maybe need to run it through a MP3 application and export the file again. Very hard to know at the moment what the problem is you have. I cannot hear anything really in the audio of the video clip you put up either - might be easier for you to know what to hear for as you know its there.



    • #3
      Hello James and thanks for your help.
      the files have not been normalised but they have the same level. (Iv'e allready checked under sony soundforge 9 when I got the problem)
      here is one of the files with the problem:
      it directly came from the sdcard

      and i'm using my function to call it
      somo_play_folder_track(22,170); //SAY ACCESS GRANTED

      my next test will be to test another mp3 compressor but the problem appears even using uncompressed wave files (so I'm pretty sure the mp3 compressor is not the problem).

      Do you have more details about the delay required to execute each command? It will be helpfull to build a reliable code library
      Last edited by Genesis; 4 March 2015, 05:39 PM.


      • #4
        Hi Genesis

        Here is a bit of a writeup that was done by one of our engineers a little while ago.
        Unfortunately this was never included in the Datasheet - I will get that organised.

        Please have a read, hopefully it contains useful information for you.

        I will arrange a test using the file you sent also.
        How many SOMO-II's do you have? Is it just the one which you are having problems with?
        I am still not 100% sure of what the problem is. Is it just this file is lower/higher volume than other files when played on the SOMO-II, or is the volume changing during playback of this one song.
        Please advise

        Attached Files


        • #5
          Thank you for the file James.
          I have two modules and I have tried on both of them with same results unfortunately.
          the strange thing is that it's not sonstant. not on each file. like random.
          you know it's like an automatic gain control decreasing the gain when it detect a peak. with compression of the signal
          Last edited by Genesis; 5 March 2015, 04:50 AM.


          • #6
            hmm, maybe try lowering the gain/volume of the file and compensating by increasing the volume of the module?


            • #7
              If I have free time this weekend I will try more tests and measure the output with a scope


              • #8
                Hi Genesis,

                I tested the mp3 file the link of which you posted above. I didn't notice anything wrong with the playback volume. That was my perception at least. My setup was far simpler however.

                Click image for larger version

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                I used a small 8-ohm speaker. The serial commands were sent thru a 4D USB programming cable. See attached photo.



                • #9
                  Thanks Doff for your test.The volume go down when the french word "activé" is played. we can heard more "acTIVE" where "ac" is missing
                  I've taken the time this morning to make measures.

                  About my system the SDcard contain near 1395 files in 31 directories and never over 255 files in each (perhaps it makes the difference but I can test with only one file).
                  now here is the original wave file opened under soundforge. to get an idea of the envelope
                  Click image for larger version

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                  and here is what I've measured at the output in parallel of the speaker with my scope (differential measure beetwin channel 1 and channel 2 ac coupled + math operation to avoid audio amplifier short circuit to ground)
                  Click image for larger version

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                  and here is a zoom of the last part where I found the volume very low:
                  Click image for larger version

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                  Last edited by Genesis; 7 March 2015, 09:06 PM.


                  • #10
                    and here the comparison between the original wave opened under soundforge and the measured envelope: Click image for larger version

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                    As you can see something is missing. I don't know why but the wave file is troncated. If that can help to find why.
                    Last edited by Genesis; 7 March 2015, 08:49 PM.


                    • #11
                      here is another test with only one file on the sdcard.
                      iit's another one saying "acces autorisé".
                      and here is the comparison:
                      the original one from soundforge
                      Click image for larger version

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                      and the measured signal
                      Click image for larger version

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                      Attached Files


                      • #12
                        And here is a comparison to fit with the soundforge timeline (file is 1.062s long) between the two blue cursors (dt=1.060s)
                        Click image for larger version

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                        the first 50ms of the wave are compressed! it's the little glitch. so the volume for this part is low as described for this issue.

                        The voice say near the same word in french as the one above.
                        "activé" for the one above and "acces" for this one.

                        The file was duplicated in wav and mp3, normalized, mono, stereo with exactly same results.
                        note: 24bits depht wave file doesn't work
                        Last edited by Genesis; 7 March 2015, 10:38 PM.


                        • #13
                          listen carefully the attached file.

                          it was a recording made with my samsung phone.
                          the module is playing two files in continuous mode.
                          the "acces autorisé" words and an fx door sound used as "separator".
                          they are played 8 times
                          as you can ear the module doesn't play exactly the same sound.
                          the first loop is not good
                          the second one is near correct
                          the third not
                          the fourth near correct
                          the loop 5 is not good
                          and the 3 lasts are good
                          the 7 is perfect.
                          strange thing uuuh?
                          Last edited by Genesis; 8 March 2015, 03:25 AM.


                          • #14
                            any ideas?


                            • #15
                              Hi Genesis,

                              What SOMO-II hardware revision do you have?