Information Technology Reference
In-Depth Information
When processing digital audio or image data the gain of the system will need to be variable so that mixes and
fades can be performed. Gain is controlled in the digital domain by multiplying each sample value by a coefficient.
If that coefficient is less than one, attenuation will result; if it is greater than one, amplification can be obtained.
Figure 2.41:
Two configurations which are common in processing. In (a) the feedback around the adder adds the
previous sum to each input to perform accumulation or digital integration. In (b) an invertor allows the difference
between successive inputs to be computed. This is differentiation.
Multiplication in binary circuits is difficult. It can be performed by repeated adding, but this is too slow to be of any
use. In fast multiplication, one of the inputs will be simultaneously multiplied by one, two, four, etc., by hard-wired
bit shifting.
Figure 2.42
shows that the other input bits will determine which of these powers will be added to
produce the final sum, and which will be neglected. If multiplying by five, the process is the same as multiplying by
four, multiplying by one, and adding the two products. This is achieved by adding the input to itself shifted two
places. As the wordlength of such a device increases, the complexity increases exponentially.
