Audio Coder (AC)

AC delivers high-quality compressed audio signal at low data rates. AC is useful for digital music recording and playback for many applications including portable game devices, toys, educational devices, handheld A/V devices, e-books and wireless microphone.

AC is currently available for two signal bandwidths: 4- and 7-kHz, with corresponding sample rate at 8 and 16 kHz, respectively. AC-4 achieves 11:1 compression ratio (from the original audio data rate at 128 kbit/s to the compressed rate at 12 kbit/s), while AC-7 achieves 13:1 compression ratio (from the original audio data rate at 256 kbit/s to the compressed rate at 20 kbit/s).

Comparing speech coder and audio coder such as SC vs. AC, SC can achieve much higher compression ratio, as human speech production mechanism can be well represented by very compact parametric models, while audio (music) signal comprises many different sound sources and cannot be represented by such compact parametric models.

FEATURES

• User-selectable multiple data rates:

  - AC-4: 6/7/8/9/10/11/12 kbit/s; with 12 kbit/s as normal operating data rate.

  - AC-7: 12/13/14/15/../30/31/32 kbit/s; with 20 kbit/s as normal operating data rate.

• - I/O format: 16 bit/sample linear PCM, 8-kHz (AC-4) and 16-kHz (AC-7) sample rate.