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- Original AC-2: fixed factor of 6 ``transparent'' compression for 44.1kHz 16-bit audio
- Now adjustable from 64 to 192 kilobits/sec/channel (ratios from 11 to 3.7
for 44.1kHz 16-bit audio)
- Mono algorithm (no use of stereo correlation)
- Can decode 2 channels in real time on 1 Motorola DSP5600x at 25MHz
- Uses Princen-Bradley Filterbank (DCT,DST)
- FFT can be used to compute DCT and DST for speed
- Nominal frame size = 512 samples at 44.1kHz (12ms)
- Second frame size (128) chosen for transients
- 256 FFT bins partitioned into 40 critical bands
- Masking pattern estimated
- One exponent per critical band (K. Brandenburg)
- Mantissa bit allocation based on signal to masking ratio
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Download Compression.pdf
Download Compression_2up.pdf
Download Compression_4up.pdf
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