High Quality Switched Discrete Cosine
Transform and Wavelet Packet
Audio Coding Technique
We propose a hybrid coding system that utilizes both Wavelet
Packet (WP) and DCT techniques. To process each audio frame, the
system selects either WP or DCT to process based on the frame
flatness measures in wavelet domain and frequency domain. If DCT
is chosen, all DCT coefficients are quantized by a non-uniform
quantizer according to the frequency masking curve. On the other
hand, frame data are segmented into 26 fixed subbands when WP is
chosen. Then, the system selectively utilizes DCT to promote
frequency resolution of each subband based on the subband
flatness measure. By quoting optimal bit-allocation for
non-ideal filter bank, the masking threshold from psychoacoustic
model can be translated into specific criteria in the wavelet
domain for quantization. Experiment results show that the
proposed system is superior to MP3 and AAC LC profile at 64k
bps.
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