BM28723AMUV
Description of Function - continued
14 Digital Sound Processing (DSP)
The digital sound processing (DSP) part of BM28723AMUV is composed of special hardware which is optimal for TV and
Mini/Micro Component System. BM28723AMUV does the following processing using this special DSP.
Pre-Scaler, Channel mixer, 12 Band BQ, Fine Master Volume, 3 Band DRC, Fine Post-scaler,
DC Cut HPF, Hard Clipper
The outline and signal flow of the DSP part
Data width:
Machine cycle:
Multiplier:
32 bit (DATA RAM)
20.3ns (1024fS, fs=48kHz)
32x24 → 56 bit
Data
RAM
In
MUX
Adder:
Data RAM:
56+56 → 56 bit
512x32 bit
0
Coef
RAM
Coefficient RAM:
Sampling frequency:
512x24 bit
fs=32k, 44.1k, 48kHz
MUX
Decorder
ADD
Acc
Out
I2S
LJ
RJ
Fine
post
scaler/
ch
Fine
Pre
Scaler
Chanel
Mixer
DC cut
HPF
Hard
Clipper
3Band
DRC
Post
Scaler
12Band
/ch BQ
Input1
Main
Master
Volum
e/ch
Figure 51
Digital signal from 16bit to 24bit is inputted to the DSP but extends 8bit (+48dB) as the overflow margin to the MSB side.
When the processing is over this range, it will be clip processing inside DSP. Note that in case of commonly used second
IIR-type (BQ) filter is the digital filter, output of the internal multiplier and adder will consume a lot of overflow margin.
The output of multipliers and the adder might exceed +48dB by the
coefficient of a1, a2, b0, b1, and b2. In that case, data becomes
saturation output. Therefore, the output of the filter cannot obtain
the aimed characteristic.
X[n]
Y[n]
b0
b1
b2
Z-1
Z-1
Z-1
X[n-1]
a1
a2
Y[n-1]
Z-1
X[n-2]
Y[n-2]
-1 is multiplied by the coefficient of a1 and a2.
Considering efficiency of calculation at DSP.
Direct form 1
Figure 52
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31.Aug.2018 Rev.001
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