Audio Signal Processing and Coding

COMPUTER EXERCISES

Use the speech file ‘Ch2speech.wav’ from the Book Website for all the computer exercises in this chapter.

2.24. Consider the 2-band QMF bank shown in Figure 2.35. In this figure, x(n) denotes speech frames of 256 samples and denotes the synthesized speech frames.

1. Design the transfer functions, F₀(z) and F₁(z), such that aliasing is cancelled. Also calculate the overall delay of the QMF bank.
2. Select an arbitrary voiced speech frame from Ch2speech.wav. Give time-domain and frequency-domain plots of x_d0(n) and x_d1(n) for that particular frame. Comment on the frequency-domain plots with regard to low-pass/high-pass band-splitting.

   

   Figure 2.35. A two-band QMF bank.

   

   Figure 2.36. Speech synthesis from a select number (subset) of FFT components.

   Table 2.2. Signal-to-noise ratio (SNR) and MOS values.

   

3. Repeat step (b) for x₁(n) and x_d1(n) in order to compare the signals before and after the downsampling stage.
4. Calculate the SNR between the input speech record, x(n), and the synthesized speech record, . Use the following equation to compute the SNR,

   Listen to the synthesized ...