Transcoding yes or no?


My trunk supports alow and ulow.
My freepbx and my phones support G722. Do I enable G722 on the phones and let asterisk transcode the audio for the trunk? Or do I disable G722 until my trunk starts supporting it?
I don’t do internal calls.

If my phone uses alow and my trunk alow does freepbx still transcode the call?

(Joshua C. Colp) #2

It depends on the codec preference order and what is actually negotiated. If it does transcode, g722 and ulaw are extremely cheap to transcode between. Unless you are under an extremely tight environment it’s premature to worry about any transcoding costs between the two.

(David55) #3

The PSTN, itself, uses µ-law in North America, and A-law in most other places, so G.722 is not going to give you any advantage in the foreseeable future, for PSTN calls.


I only care about quality loss.
Do I notice. G722 -> ULAW
How about Ulaw -> G722


Most calls I receive are from phones. On GSM 4G I see the HD logo on my phone. I asume that quality is superior to ulaw?

BTW: I’m in europe

(Joshua C. Colp) #6

No, you would not notice quality loss.


Thx this answers my question :slight_smile:

(David55) #8

GSM is considerably lower quality, than any of them, and, in particular, isn’t really suitable for music. I’m not sure whether GSM HD implies something radically different from GSM, or something that is similar but a bit better.

It turns out that G.722 is not a clear winner over G.711 (µ-law and A-law), even for speech; it depends on the people using it. See


Over here HD Audio on GSM means: Adaptive Multi-Rate Wideband AMR-WB G.722.2

(David55) #10

OK. The G722 in the name doesn’t mean it is anything like G722 without a suffix. The Wikipedia article on it suggests that, for speech only communication, it matches G722 quality at about 56kbps, but mobile networks don’t use it at anything like that rate. It’s a vocoder type codec, so unlikely to do well on music.


We don’t have music playing on our system. We just receive calls from customers who like to buy something. So it is key to hear them clearly if they give you the adress or a date.

(David55) #12

The weakest link will be the customer’s mobile phone.

If you had end to end G.722, which you won’t get over the public network, it would make it easier to distinguish between f and s sounds. The main impact of G.722 over G.711 will only apply for calls which are internal to your system.

(system) closed #13

This topic was automatically closed 31 days after the last reply. New replies are no longer allowed.