++Quantizing LPC Filter Coefficients
Quantizing to fewer than 64 levels (6 bits) quickly results in an unintelligible signal. At 64 levels there is still a high-pitched blip during the "ch" of the word "watch", where the predictive coding doesn't predict very well. Lower quantizations result in mostly silence with a blip in the same place. The intelligibility is definitely not a monotonic function of quantization levels, though. For instance, with 40 levels the voice is still very intelligible, but with 49 there's almost nothing.
++LSPs
Quantizing the LSP representation breaks down much more gracefully, and is easily understandable down to about 16 quantization levels(4 bits)
++Quantizing the Residual
Resynthesis after quantizing the normalized residual down to 16 levels(4 bits) with the original filter coefficients still sounds OK, with audible distortion. At 64 levels it sounds pretty good.
++Multi-Pulse Excitation
Using multi-pulse excitation sounds pretty decent at 16, and even at 8 it's not bad.
Assignment 7
