VoIP Bandwidth and Microphones
When using the Nellymoser codec, one microphone might produce more bandwidth over against another. Nellymoser accepts five different microphone rates values: 5, 8, 11, 22 and 44. Each of these rate values consumes bandwidth of roughly double its value. For example the 8kHz setting consumes roughly 16kbps and 11kHz setting consumes roughly 22 kbps. The default rate value is 8kHz. This may vary depending on the sound capture device in use.
The Flash Player microphone reference documentation reads:
“The default value is 8 kHz if your sound capture device supports this value. Otherwise, the default value is the next available capture level above 8 kHz that your sound capture device supports, usually 11 kHz.”
It is possible for two different microphones to consume different amounts of bandwidth.
In case of the Speex codec, it has a fixed sampling rate of 16kHz. Speex allows control of the quality by offering us 11 different encoding quality options. See the following reference table :
| Speex | NellyMoser | ||
| Quality (EncodeQuality)Mic rate is fixed at 16 | Bandwidth(kbps) | Quality (Mic Rate) | Bandwidth (kbps) |
| 0 | 3.95 | 5 | 11.025 |
| 1 | 5.75 | 8 | 16 |
| 2 | 7.75 | 11 | 22.05 |
| 3 | 9.80 | 22 | 44.1 |
| 4 | 12.8 | 44 | 88.2 |
| 5 | 16.8 | ||
| 6 | 20.6 | ||
| 7 | 23.8 | ||
| 8 | 27.8 | ||
| 9 | 34.2 | ||
| 10 | 42.2 | ||
Adobe Connect supports three Speex settings:
- Fast : Encode Quality 4
- Good : Encode Quality 6
- Best : Encode Quality 8
Increasing the encoding quality will increase the quality of the stream but will also require greater bandwidth. The Speex codec is optimized for voice and also includes voice activity detection that allows it to reduce bandwidth.