5a92aa8440
The implementation is a FIR filter bank with DCT modulation, similar to the proposed in "Multirate Signal Processing for Communication Systems" by Fredric J Harris. The lowpass filter prototype has these characteristics: * Passband ripple = 0.3dB * Passband frequency = 0.147 (7kHz at 48kHz) * Stopband attenuation = 40dB * Stopband frequency = 0.192 (9.2kHz at 48kHz) * Delay = 24 samples (500us at 48kHz) * Linear phase This filter bank does not satisfy perfect reconstruction. The SNR after analysis and synthesis (with no processing in between) is approximately 9.5dB depending on the input signal after compensating for the delay. The performance on my workstation of AudioProcessing (with AGC and NS enabled) on a 413s recording compared to previous versions is as follows: * Input signal has 32kHz sample rate: 3.01s * Resampling 48kHz to 32kHz: 3.56s * Today's temporary filter bank: 5.67s * This filter-bank: 4.62s BUG=webrtc:3146 R=andrew@webrtc.org, bjornv@webrtc.org Review URL: https://webrtc-codereview.appspot.com/48999005 Cr-Commit-Position: refs/heads/master@{#9090}