DSP Blockset

Quantizing an Input Signal

In the previous topic, Creating a Scalar Quantizer, you learned how to create scalar quantizers using the Scalar Quantizer Design block. In this topic, you learn how to use these scalar quantizers to quantize the residual and the reflection coefficients in the dsplpc demo model. This topic assumes that you completed the procedures described in Creating a Scalar Quantizer:

1. Copy the Scalar Quantizer - Reflection Coefficients block, and paste the copy of the block into your model file.
2. Copy the Scalar Quantizer - Residual block, and paste the copy of the block into your model file.

1. Your model should now look similar to the following.
   
   

3. Double-click the Scalar Quantizer - Residual1 block.
4. From the Quantizer mode list, choose Decoder.

1. Note that the Scalar Quantizer Design block sets the Codebook parameter for you. The Scalar Quantizer Design block has also set the Boundary points parameter in the Encoder blocks.

5. Click OK.
6. Double-click the Scalar Quantizer - Reflection Coefficients1 block.
7. From the Quantizer mode list, choose Decoder. Click OK.
8. Connect the blocks so your model looks similar to the following figure.
   
   
9. Simulate your model.
10. Double-click the Original Signal and Processed Signal blocks, and listen to both the original and the processed signal.

1. Again, there is almost no difference between the two. You can therefore conclude that quantizing your residual and reflection coefficients did not impact the ability of your system to accurately reproduce the input signal.

   In this implementation, the bit rate is 64.4 kbits per second. This is higher than most modern speech coders, which typically have a bit rate of 8 to 64 kbits per second. If you decrease the number of bits allocated for the storage of the reflection coefficients or the residual signal, the speech quality would degrade.

You have now quantized the residual and reflection coefficients in the LPC Analysis and Synthesis of Speech demo model. For more information about quantizers, see the following block reference pages: Scalar Quantizer and Scalar Quantizer Design.

Creating a Scalar Quantizer

Deconstructing Signals