AD1954 Analog Devices, AD1954 Datasheet - Page 22

• Manufacturer Part Number: AD1954
• Description: SigmaDSP Digital Audio Processor
• Manufacturer: Analog Devices

AD1954
Bit 8 is used to enable the three serial output pins. These pins
are connected to the output of the serial input MUX, which is
set by bits <7:6>. The default is 0 (disabled).
Volume Registers
The AD1954 contains three 22-bit volume registers, one each
for the left, right, and subwoofer channels. These registers are
special because when the volume is changed from an initial value
to a new value, a linear ramp is used to interpolate between the
two values. This feature prevents audible clicks and pops when
changing volume. The ramp is set so that it takes 512 audio
frames to decrement from a volume of 1.0 (default) down to 0
(muted). The volume registers are formatted in 2.20 two’s
complement, meaning that 01000000000000000000 is interpreted
as 1.0. Negative values can also be written to the volume register,
causing an inversion of the signal. Negative values work as ex-
pected with the “ramp” feature; to go from +1.0 to –1.0 will take
1024 LRCLKs, and the volume will pass through 0 on the way.
Parameter RAM Contents
Table VI shows the contents of the parameter RAM. The
parameter RAM is 22 bits wide, and occupies SPI addresses
Address
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
PRELIMINARY TECHNICAL DATA
Function
IIR0 Left b0
IIR0 Left b1
IIR0 Left b2
IIR0 Left a1
IIR0 Left a2
IIR1 Left b0
IIR1 Left b1
IIR1 Left b2
IIR1 Left a1
IIR1 Left a2
IIR2 Left b0
IIR2 Left b1
IIR2 Left b2
IIR2 Left a1
IIR2 Left a2
IIR3 Left b0
IIR3 Left b1
IIR3 Left b2
IIR3 Left a1
IIR3 Left a2
IIR4 Left b0
IIR4 Left b1
Table VI. Parameter RAM Contents
0 – 255. The low addresses of the RAM are used to control the
biquad filters. There are 22 biquad filters in all, and each
biquad has five coefficients, resulting in a total memory usage
of 110 coefficients. There are also two tables of 33 coefficients
each that define the main and sub compressor input/output
characteristics. These are loaded with 1.0 on power-up, resulting
in no compression. Other RAM entries control other compressor
characteristics, as well as delay and spatialization settings.
The parameter RAM is initialized on power-up by an on-board
boot ROM. The default values (shown in the table) yield no
equalization, no compression, no spatialization, no delay, and
“normal” detector time constants in the compressor sections.
The functionality of the AD1954 on power-up is basically that
of a normal audio DAC with no signal-processing capability.
The data format of the Parameter RAM is two’s complement
2.20 format. This means that the coefficients may range from
+2.0 (–1 LSB) to –2.0, with 1.0 represented by the binary word
01000000000000000000.
Default value in fractional 2.20 format
1.0
0
0
0
0
1.0
0
0
0
0
1.0
0
0
0
0
1.0
0
0
0
0
1.0
0