LPC Vocoder GUI ver. 1.0

An interactive LPC Vocoder with several options.

An LPC vocoder (Linear-Predictive Coder), is a lossy compression technique that is highly optimized for low-bitrate speech transmission.

The problem here that we solve is to take a speech waveform with an 8kHz sampling rate, code it to a much lower bit-rate so that it can be transmitted over a channel, and finally decode it to a signal that is of the same quality.

To do this we take advantage of the fact that the human vocal tract can be modelled as a linear system for a period of about 25 ms. We estimate the spectrum of the vocal tract in frames of 25 ms (see LPC analysis) and estimate the pitch of the speech once every 10 ms. We then transmit this data, which is much less than transmitting 8000 samples every second.

To reproduce the speech we simply excite the estimated spectrum with an impulse train of the estimated pitch.