How do I adjust the gain levels on DAHDI channels?

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Answer
If the audio levels on your DAHDI channels seem to be lower than they should be, you can adjust the gain levels within the Asterisk configuration to compensate for this.
  1. Modify the /etc/asterisk/chan_dahdi.conf file
  2. Find the rxgain and txgain settings -- these will control the receive and transmit gain levels, respectively
  3. To begin with, it's best to use small increments when changing the gain levels. We'd recommend going in increments of 2
    • Note: By default, both rxgain and txgain are set at 0. You can increase the gain by using a positive number, and decrease it using a negative number. The numbers represent db (decibels), so a value of 4 would mean the gain is increased by 4 db.
  4. For example, if the audio levels are too quiet we would try increasing the gain: for outgoing audio, set txgain=2 to increase it by 2 db; for the incoming audio, you would set rxgain=2
  5. Save the chan_dahdi.conf file
  6. Restart Asterisk for the change to take effect
  7. Place some test calls to see if the audio levels are where you need them. If not, go back to step 1 and repeat the process to get the gain levels to where you need them