Digital Signal Processing Reference
In-Depth Information
Band 2
1.
Run the bandpass filter two times and sum with the two previous outputs
stored in
B
2
from band 1.
2.
Store the summed values in
B
2
at the same locations 1 and 2 (again).
3.
Pass the sample in
B
2
at location 1 to the interpolation filter twice and obtain
two outputs.
4.
Store these two outputs in buffer
B
3
, size 256, at locations 1 and 2.
5.
Pass the sample in
B
2
at location 2 to the interpolation filter twice and obtain
two outputs.
6.
Store these two outputs in buffer
B
3
at locations 3 and 4.
Band 3
1.
Run the bandpass filter four times and sum with the previous four outputs
stored in
B
3
from band 2.
2.
Store the summed values in
B
3
at locations 1 through 4.
3.
Pass the sample in
B
3
at location 1 to the interpolation filter twice and obtain
two outputs.
4.
Store these two outputs in buffer
B
2
at locations 1 and 2.
5.
Pass the sample in
B
3
at location 2 to the interpolation filter twice and obtain
two outputs.
6.
Store these two outputs in buffer
B
2
at locations 3 and 4.
7.
Repeat steps 3 and 4 for the other two samples at locations 3 and 4 in
B
3
.For
each of these samples, obtain two outputs, and store each set of two outputs
in buffer
B
2
at locations 5 through 8.
Bank 10
1.
Run the bandpass filter 512 times and sum with the previous 512 outputs
stored in
B
2
from band 9.
2.
Store the summed values in
B
2
at locations 1 through 512.
No interpolation is required for band 10. After all the bands are processed, wait
for the output buffer
B
1
, size 512, to be empty. Then switch the buffers
B
1
and
B
2
—
the last working buffer with the last output buffer. The main processing is then
repeated.
The multirate filter was implemented on the C25 processor using 9 bands and on
the C30 processor using 10 bands [8], and can be transported to the C6x. Using a
total of 30 different levels, any specific
3
-octave filter can be turned on or off. For
example, all the filter bands can be turned on except bands 2 and 5. Figure 10.62
shows the frequency response of the three
3
-octave filters of band 9 implemented
on the C30. Note that if a sampling rate of 8 kHz is set (for the highest band), the
middle
3
-octave band 1 filter would have a center frequency of 4 Hz (one-fourth of
the equivalent sampling rate for band 1).
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