Objectives:
This chapter studies speech quantization and compression techniques such as signal companding, differential pulse code modulation, and adaptive differential pulse code modulation. The chapter continues to explore the discrete-cosine transform (DCT) and modified DCT and shows how to apply the developed concepts to understand the MP3 audio format. The chapter also introduces industry standards that are widely used in the digital signal processing field.
As we discussed in Chapter 2, in the digital signal processing (DSP) system, the first step is to sample and quantize the continuous signal. Quantization is the process of rounding off the sampled signal voltage to the predetermined levels that will be encoded by analog-to-digital conversion (ADC). We have described the quantization process in Chapter 2, in which we studied unipolar and bipolar linear quantizers in detail. In this section, we focus on a linear midtread quantizer, which is used in digital communications (Roddy and Coolen, 1997; Tomasi, 2004), and its use to quantize speech waveform. The linear midtread quantizer is similar to the bipolar linear quantizer discussed in Chapter 2 except that the midtread quantizer offers the same decoded magnitude range for both positive and negative voltages.
Let us look at a midtread quantizer. The characteristics and binary codes for a 3-bit midtread quantizer are depicted in Figure 11.1, where the code is in a sign magnitude format. Positive voltage is coded using a sign bit of logic 1, while negative voltage is coded by a sign bit of logic...
TABLE OF CONTENTS 
