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U. Glaeser

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FIGURE 27.17 Efficient audio (and speech) compression by exploiting the knowledge about the audio (and speech)<br />

production and perception: (a) coder scheme, (b) decoder scheme.<br />

27.6 Digital Audio Signal Processing Systems<br />

Fast development of very large scale integration (VLSI) electronics chips (digital signal processors (DSPs),<br />

ADCs and DACs, audio codecs, etc.) gives the possibility of effective digital processing of audio signals. The<br />

general scheme of a digital audio processing system is shown in Fig. 27.16. Using novel facilities of DSPs,<br />

not only sophisticated digital filters and filter banks, but also whole audio codecs can usually be realized in<br />

real time with a single processor, i.e., without the necessity of using expensive multiprocessor systems.<br />

Real-time implementation of DSP algorithms is possible due to new features of modern DSPs [7].<br />

Among the most important are:<br />

• Hardware multiplier and long accumulator<br />

• Hardware type and multibus architecture<br />

• An on-chip memory with no additional wait state cycles<br />

• Time division multiplexed (TDM) port for communication between multiple DSPs<br />

• Bit-reversed addressing used in fast Fourier transformation (FFT) algorithms<br />

• Circular buffers—a key feature of many DSP routines (e.g., in the realization of finite impulse<br />

response (FIR) digital filters)<br />

• Multiple data registers important, e.g., for storing of temporary data<br />

New facilities of modern DSPs give the possibility for substantial reduction of the number of operations.<br />

A single DSP processor can be used for multichannel and/or multitasking applications, both realized in<br />

© 2002 by CRC Press LLC<br />

PCM<br />

speech<br />

PCM<br />

audio<br />

Bit<br />

stream<br />

Analysis<br />

Speech<br />

source<br />

model<br />

Audio<br />

source<br />

model<br />

?<br />

Analysis<br />

Decoding<br />

(a)<br />

(b)<br />

Coding<br />

Psychoacoustic<br />

auditory<br />

perception<br />

model<br />

Coding<br />

Synthesis<br />

Bit<br />

stream<br />

Bit<br />

stream<br />

PCM<br />

audio (or speech)

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