LPC speech coding based on variable-length segment quantization

A parametric prosody coding approach for Mandarin speech using a hierarchical prosodic model

“…Therefore, segment-based speech coders, such as segment vocoders [11][12][13][14][15][16][17][18][19][20][21][22][23], phonetic vocoders [24][25][26][27][28][29][30][31][32][33], and text-to-speech (TTS)-based speech coders [34][35][36], were proposed to overcome this limitation. Those coders generally process speech at segment level instead of sample or frame level.…”

“…For segment-based speech coding, the prosodic information associated with each segmental unit is usually encoded directly after quantization without considering underlying prosodic models. Methods proposed for encoding segmental pitch contour include scalar-quantization of segmental mean value [11,13] or values at segmental end points [17], vector-quantization [25,31], scalar-quantization after being parameterized by piecewise linear approximation (PLA) [12,18,19,24,32,33,36], the frame-by-frame scheme as used in the frame-based coder [14,15,21,23,27,28], and quantization by using stored pitch contour patterns [34]. For segment duration, it is usually directly encoded/scalar-quantized [11, 12, 15, 17-19, 23, 24, 26-28], or vector-quantized [29][30][31][32][33].…”

“…Predictive VQ [40] was proposed to further reduce the bit-rate by using the property of inter-frame spectral redundancy or correlation. For segment vocoders [11][12][13][14][15][16][17][18][19][20][21][22][23], the main study issues focused on the choice of segmental units, the realization of segmentation and segment quantization, and the design of segment codebook. For phonetic vocoders [24][25][26][27][28][29][30][31][32][33], the studies mainly focused on the choice of acoustic unit for speech recognition/synthesis [24][25][26][27] and speaker adaptation of spectral information [28,30,32,33].…”

“…A segment vocoder of fixed length simply quantizes a sequence of speech segments of l frames (l > 1) by matrix quantization (MQ) [14,22]. In a variable-length segment vocoder [11][12][13][15][16][17][18][19][20][21][22][23], segmental unit is usually pre-determined in the design of speech segmenter or speech recognizer. General segmental units can be phones, di-phones, syllables, or automatically derived acoustic units.…”

“…Those coders generally process speech at segment level instead of sample or frame level. Generally, a segment vocoder [11][12][13][14][15][16][17][18][19][20][21][22][23] firstly divides the speech signal into a sequence of fixedor variable-length segments by a speech segmenter or a speech recognizer and then quantizes each segment by a codebook of pre-stored speech segments. A segment vocoder of fixed length simply quantizes a sequence of speech segments of l frames (l > 1) by matrix quantization (MQ) [14,22].…”