IP audio Gain adjustment

(New from DSP SW 01.11 / AMCD 10.31)

Audio levels and gain on AlphaCom IP audio connections may be changed using NVRAM programming. Defaults has been set, so that normal usage should work without any changes.

Background

Normal audio is encoded in AlphaCom internal digital audio format (SigmaDelta) with a fairly low level, compared to the max theoretical amplitude of the audio format. A headroom of factor 10 = 20dB is common.

For IP audio connections between AlphaComs, the SigmaDelta audio is converted to a standard format like G.722 or G.711. The gain is 1 = 0dB, in the sense that max SigmaDelta amplitude corresponds to max amplitude on the external format. The audio level on these connection will therefore be quite low.

In the telecom world, the standard audio level is much higher, headroom as small as 3dB is normal. Therefore AlphaCom audio needs to be amplified when sent to external SIP equipment.

Gain adjustment and limiter

The default behaviour is now:

• Inter-AlphaCom and to IP stations: 0dB gain (ie low audio level)
• Towards SIP: +18dB gain out towards SIP, -9db reduction for incomming audio.

module_profile.node_profile[51].audio_gain_in 
module_profile.node_profile[51].audio_gain_out
module_profile.node_profile[51].audio_limit_in
module_profile.node_profile[51].audio_limit_out

Node:

SIP node number (set for registrar and trunk)
own node: gainadjustments  for all local IP stations;
Alphacom nodes: default is no gain adjustment, but c

Value

zero: default values. For SIP node, gain is increased
Otherwise: use the specifed value, steps of 3 dB.