The figure given below shows the block diagram of voice encoder. Let us now discuss the operation of each in detail- Voice Encoder Vocoder is comprised of voice encoder and decoder. In simple words we can say, by analysing two previous samples it predicts the outcome. It is basically a technique to estimate future values. LPC is an acronym for Linear Predictive Coding. LPC is extensively used in case of speech and music application. Thus we can have a synthesised approximated speech waveform. The filter unit then filters the input in such a way so as the required letter is pronounced.
Then the selected signal is passed through a filter that simulates the effect of mouth, throat and nasal passage of speaker. The position of the switch helps in determining whether the sound is voiced or unvoiced. The noise source present in the circuit is used to simulate the unvoiced sounds. Here, voiced sounds are simulated by the impulse generator, the frequency of which is equal to the fundamental frequency of vocal cords. Unvoiced sounds are generated by expelling air through lips and teeth.Īs we can see in the above figure of speech model used in Vocoder. On contrary, the sound produced at the pronunciation of the letters such as ‘s’, ‘p’ or ‘f’ is known as unvoiced sounds. Voice sounds are basically the sounds generated by vibrations of the vocal cords. As speech contains a sequence of voiced and unvoiced sounds, this is the basis for the operation of a voice model.īefore proceeding further, it is better to first understand what is voiced and unvoiced sounds. Let’s have a look at the voice model shown below-Ī voice model is used to simulate voice. It aims to emblem the amplitude and frequency characteristic of speech signal onto the synthesis signal, while maintaining the pitch of the speech signal. The vocoder takes two signals and creates a third signal using the spectral information of the two input signals. Then other audio signals are affected by the use of that characteristic signal.
Vocoder works in such a way that it first captures the characteristic element of the signal. This reconstructed waveform at the receiver must be similar and not identical to the waveform actually transmitted. We can simply transmit the information by which one can reconstruct that particular waveform. Whenever a speech signal is transmitted, it is not needed to transmit the precise waveform.
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