ZyXEL |
There are two slightly different sets of compression algorithms implemented in the program for ZyXEL modems.
The first set includes ZyXEL ADPCM 3 and ZyXEL ADPCM 2 speech coding and proprietary algorithms. Their implementation is taken directly from ZyXEL programming library sources. Default compression method is ZyXEL ADPCM 3.
You can choose the compression method with best quality/performance for your modem. If one does not work, try another or an alternative method with different baud rate.
Another set is ZyXEL ADPCM [alternative] - an alternative implementation of the same methods. This set includes ZyXEL ADPCM 4 bps, which is otherwise not available and which gives the best compression quality. 4 bps ADPCM is not available in older ZyXEL modems.
Note that bits-per-sample regulation is only available in [alternative] set.
CELP coding is not currently implemented.
Method | Bit Depth | Sampling Frequencies | Comment |
---|---|---|---|
ZyXEL ADPCM 2 | 2 | 7200, 8000, 9600, 11025 | Poor sound quality |
ZyXEL ADPCM 3 | 3 | 7200, 8000, 9600, 11025 | Classic 3-bit ADPCM scheme |
ZyXEL ADPCM 3 (new) | 3 | 7200, 8000, 9600, 11025 | 3-bit ADPCM scheme with added sync bits in the voice data. |
ZyXEL ADPCM 4 | 4 | 7200, 8000, 9600, 11025 | Good sound quality |
IMA ADPCM (Intel/DVI) | 4 | 7200, 8000, 9600, 11025 | Standard Intel/DVI (IMA ADPCM), good sound quality |
A-law PCM 8 | 8 | 7200, 8000, 9600, 11025 | Very good sound quality |
u-law PCM 8 | 8 | 7200, 8000, 9600, 11025 | Very good sound quality (if supported) |
(*) Bold is a recommended setting. Default sample rate for ZyXEL modems if 9600 Hz.