For each frame, what's sent over to the receiver for decoding? The coefficients , pitch in some bits, voiced/unvoiced classification in another bit?
Another broad question to develop intuition about LPC and CELP for speech encoding.
By using spectral envelope estimation with LPC and related speech coders, does the bitrate reduction happen because the original fluctuations in the frequency spectrum envelope of the original audio signal require more bits to represent? And so in approximating the amplitude spectral envelope fewer bits can be used to represent the speech?
Or, the quality reduction is the result of the elimination of the spectral envelope fluctuations and the bitrate reduction results from only transmitting the LPC coefficients, pitch period, and voiced/unvoiced classification versus transmitting some stream of data for each frame, and then the receiver decodes the coefficients, voiced/unvoiced, and pitch info...?