Subject: Speech Processing

Topic: LPC and Parametric Speech Coding

Difficulty: Low

(i) The vocal tract filter is modeled as: $$ y_n = \sum_{i=1}^{10} b_i y_{n-i} + \beta y_{n-p} + G \epsilon_n $$

where, p is the pitch period and $ \beta y_{n-p} $ represents the contribution due to pitch periodicity.

(ii) The U.S federal standard 1016 specifies 4800 bps. CELP coder is given below:

a) Ten spectral parameters are updated every 30ms, consuming 34bits/11333.3 bps.

b) The pitch valve is sent after every 7.5ms. Gain is coded as 5-bits number. Pitch value is coded using 8-bits and difference in pitch coded using 6-bits. The pitch estimates costs 1600 bits.

c) The code book index is coded as 9-bits as there are 512 entries in the code book. It is sent every 7.5ms. Gain is coded using 5-bits. This require 1866.7 bps. Synchronization and error correction requires 200 bps.