What codec should I use for voice calls?
TopView voice calls over VOIP allow the specification of a codec used for encoding the audio to be used during the call. This article explains what codecs are and why you might want to use a codec that is different from the defaults used by TopView.
What is a “codec”?
From Wikipedia’s definition of Audio Codec:
An audio codec is a codec (a device or computer program capable of encoding or decoding a digital data stream) that encodes or decodes audio
Why is this a VOIP configuration option?
By default, multiple codecs are offered to the VOIP server, in order of preference, and the server will negotiate the best codec with the client.
Sometimes, the codec picked by the negotiation process may not be the best for the network or recipient devices. In these situations, you can configure TopView to specify another codec.
TopView suggests a high quality audio codec, G.722, which provides excellent calls.
If you want to test alternate codecs, we recommend starting with PCMU, PCMA, and G.729.
The codecs that will work best depend on many factors, so your experience may vary from ours. Please try many different codecs if you decide to specify custom codecs.
TopView does not provide multiple codecs as an option, choose only one custom codec for use.
TopView supports the following codecs:
| Name | Alt. name | Payload type | No. of channels | Rate (Hz) | Ratet (Hz) |
| PCMU (G.711) | PCMU | 0 | 1 | ITU-T G.711 PCM µ-Law audio 64 kbit/s | 8000 |
| PCMA (G.711) | PCMA | 8 | 1 | ITU-T G.711 PCM A-Law audio 64 kbit/s | 8000 |
| G.722 | G722 | 9 | 1 | ITU-T G.722 audio 64 kbit/s. Usually the codec in use for TopView voice calls. It is of excellent quality. | 8000 |
| G.723 | G723 | 4 | 1 | Obsoleted codec superseded by G726 | 8000 |
| G.726-16 | G726 | 104 | 1 | ITU-T G.726 audio 16 kbit/s | 8000 |
| G.726-24 | G726 | 105 | 1 | ITU-T G.726 audio 24 kbit/s | 8000 |
| G.726-32 | G726 | 106 | 1 | ITU-T G.726 audio 32 kbit/s | 8000 |
| G.726-40 | G726 | 107 | 1 | ITU-T G.726 audio 40 kbit/s | 8000 |
| G.728 | G728 | 15 | 1 | ITU-T G.728 audio 16 kbit/s | 8000 |
| G.729 | G729 | 18 | 1 | ITU-T G.729 and G.729a audio 8 kbit/s; Annex B is implied unless the annexb=no parameter is used | 8000 |
| GSM | GSM | 3 | 1 | European GSM Full Rate audio 13 kbit/s (GSM 06.10) | 8000 |
| iLBC | iLBC | 98 | 1 | Internet low Bitrate Codec 13.33 or 15.2 kbit/s | 8000 |
| L16 (2 channel) | L16 | 10 | 2 | Linear PCM 16-bit stereo audio | 44100 |
| L16 | L16 | 11 | 1 | Linear PCM 16-bit audio | 44100 |
| opus | opus | 120 | 1 | Opus audio | 48000 |
| SPEEX-Narrow | SPEEX | 97 | 1 | Speex audio | 8000 |
| SPEEX-Wideband | SPEEX | 100 | 1 | Speex audio | 16000 |
| SPEEX-Dynamic | SPEEX | 108 | 1 | Speex audio | 32000 |
Reference codecs on Wikipedia: RTP audio video profile.
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