In this section, the design of a digital audio equalizer is introduced. For an audio application such as the
CD player, the digital audio equalizer is used to adjust the sound as one desires by changing filter gains
for different audio frequency bands. Other applications include adjusting the sound source to take
room acoustics into account, removing undesired noise, and boosting the desired signal in the specified
passband. The simulation is based on the consumer digital audio processordsuch as a CD playerd
handling the 16-bit digital samples with a sampling rate of 44.1 kHz and an audio signal bandwidth at
22.05 kHz. A block diagram of the digital audio equalizer is depicted in Figure 8.24.
A seven-band audio equalizer is adopted for discussion. The center frequencies are listed in
Table 8.10. The 3-dB bandwidth for each bandpass filter is chosen to be 50% of the center frequency.
As shown in Figure 8.24, g0 through g6 are the digital gains for each banspass filter output and can be
adjusted to make sound effects, while y0ðnÞ through y6ðnÞ are the digital amplified bandpass filter
outputs. Finally, the equalized signal is the sum of the amplified bandpass filter outputs and itself. By
changing the digital gains of the equalizer, many sound effects can be produced.