Re: Troubleshooting ThumbDV HW AMBE chip with Analog_Bridge


David Ranch
 

Hello Steve,

    echo 1 > /sys/bus/usb-serial/devices/ttyUSB0/latency_timer

I'm happy to report that this resolved my issue and the audio quality issue is resolved!  If I can make a recommendation, on page 16 of https://docs.google.com/document/d/1eN50Csr29eAprBu7eKA0Bfa2XUcsXw5iktY1Ey-Qjkg/edit , consider adding tothe "Insert vocoder discussion here" section.  Something like:

   - Enable the "Project 25 IMBE Encoder/Decoder Fixed-Point implementation" codec

    This is the default setting and generally has good audio quality

    Analog_Bridge.ini

          [GENERAL]
          decoderFallBack = true
          useEmulator = false
          [DV3000]
          ;server = /dev/ttyUSB0                 ; Device of DV3000U on this machine
          ;port = 460800                         ; Baud rate of the dongle
          ;serial = true                         ; Use serial (DV3000U) or IP


   - Enable the md380-emu codec

    This has good audio quality (possibly better than the IMBE software vocoder):

       Document how the md380-emu process will be started

       Analog_Bridge.ini

          [GENERAL]
          decoderFallBack = false
          useEmulator = true
          [DV3000]
          ;server = /dev/ttyUSB0                 ; Device of DV3000U on this machine
          ;port = 460800                         ; Baud rate of the dongle
          ;serial = true                         ; Use serial (DV3000U) or IP


   - Enable HW AMBE codec

    This is the default setting and generally has good audio quality (possibly better than the IMBE software vocoder):


      - Connect the HW device directly to your computer (no USB hubs if possible)

      - Edit the Analog_Bridge.ini
          [GENERAL]
          decoderFallBack = false
          useEmulator = false
          [DV3000]
          server = /dev/ttyUSB0                 ; Device of DV3000U on this machine
          port = 460800                         ; Baud rate of the dongle
          serial = true                         ; Use serial (DV3000U) or IP



      - If used with a Raspberry Pi and you experience audio issues:

         - When connected to the Raspberry Pi, run the "dmesg" command and confirm which serial port it's beeing
          seen as.  The default is /dev/ttyUSB0 unless that device is already in use

         - Make sure that the serial RX/TX LEDs are lighting up on the USB device when receiving / transmitting signals

         - You might need to change your USB latency with:
          echo 1 | sudo tee /sys/bus/usb-serial/devices/ttyUSB0/latency_timer

         - Use a proper power supply for your Rpi as the AMBE chips are reknown for being very sensitive to
          voltage sags

--David
KI6ZHD

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