Codec 2 consists of 3200, 2400, 1600, 1400, 1300, 1200, and 700 bit/s codec modes. It outperforms most other low-bitrate speech codecs . For example, it uses half the bandwidth of Advanced Multi-Band Excitation to encode speech with similar quality. The speech codec uses 16-bit PCM sampled audio, and outputs packed digital bytes. Likewise, you send it packed digital bytes, and it outputs PCM sampled audio. The audio sample rate is fixed at 8 kHz. Internally, the codec algorithms operate on 10 ms PCM frames, with each of these audio segments declared voiced (vowel) or unvoiced (consonant).