Hi What is the "Mode"? Should I set it in program for setting the bit rate and quality? Or I only need to set the quality? At the bottom of the following page: http://www.speex.org/docs/manual/speex-manual/node10.html In Table 4: Quality versus bit-rate: Mode Quality Bit-rate (bps) mflops Quality/description 0 - 250 0 No transmission (DTX) 1 0 2,150 6 Vocoder (mostly for comfort noise) 2 2 5,950 9 Very noticeable artifacts/noise, good intelligibility 3 3-4 8,000 10 Artifacts/noise sometimes noticeable 4 5-6 11,000 14 Artifacts usually noticeable only with headphones 5 7-8 15,000 11 Need good headphones to tell the difference 6 9 18,200 17.5 Hard to tell the difference even with good headphones 7 10 24,600 14.5 Completely transparent for voice, good quality music 8 1 3,950 10.5 Very noticeable artifacts/noise, good intelligibility 9 - - - reserved 10 - - - reserved 11 - - - reserved 12 - - - reserved 13 - - - Application-defined, interpreted by callback or skipped 14 - - - Speex in-band signaling 15 - - - Terminator code