ADAV400 datasheet(18/36 Pages) AD

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ADAV400

Rev. 0 | Page 18 of 36

SIGNAL PROCESSING

The ADAV400 is designed to provide all the signal processing

functions commonly used in stereo or multichannel playback

systems. The signal processing flow is created using a graphical

development tool supplied by Analog Devices, which allows fast

development of even complex audio flows and real-time control

of all signal-processing functions.

The input and output word lengths are 24 bits. Four extra head-

room bits are used in the processor to allow internal gains of up

to 24 dB without clipping.

The signal processing blocks can be arranged in a custom program

that is loaded to the RAM of the ADAV400. The available signal

processing blocks are outlined in the Numeric Formats and

Programming sections.

NUMERIC FORMATS

It is common in DSP systems to use a standardized method of

specifying numeric formats. Fractional number systems are

specified by an A.B format, where A is the number of bits to the

left of the decimal point and B is the number of bits to the right

of the decimal point.

The ADAV400 uses the same numeric format for both the

coefficient values (stored in the parameter RAM) and the signal

data values.

Numeric Format: 5.23

Range:

−16.0 to (+16.0 − 1 LSB)

Examples:

1000 0000 0000 0000 0000 0000 0000 = −16.0

1110 0000 0000 0000 0000 0000 0000 = −4.0

1111 1000 0000 0000 0000 0000 0000 = −1.0

1111 1110 0000 0000 0000 0000 0000 = −0.25

1111 1111 1111 1111 1111 1111 1111 = (1 LSB below 0.0)

0000 0000 0000 0000 0000 0000 0000 = 0.0

0000 0010 0000 0000 0000 0000 0000 = +0.25

0000 1000 0000 0000 0000 0000 0000 = +1.0

0010 0000 0000 0000 0000 0000 0000 = +4.0

0111 1111 1111 1111 1111 1111 1111 = (+16.0 − 1 LSB)

The serial port accepts up to 24 bits on the input and is sign-

extended to the full 28 bits of the core. This allows internal

gains of up to 24 dB without encountering internal clipping.

A digital clipper circuit is used between the output of the DSP

core and the serial output ports (see Figure 22). This clips the

top four bits of the signal to produce a 24-bit output with a

range of +1.0 (−1 LSB) to −1.0.

4-BIT SIGN EXTENSION

DATA IN

SERIAL PORT

1.23

5.23

SIGNAL PROCESSING

(5.23 FORMAT)

DIGITAL

CLIPPER

5.23

1.23

Figure 22. Numeric Precision and Clipping Structure

PROGRAMMING

On power-up, the default program of the ADAV400 passes the

unprocessed input signals to the outputs, but the outputs are

muted by default. There are 2560 instruction cycles per audio

sample. This DSP runs in a stream-oriented manner, meaning

all 2560 instructions are executed each sample period. The

ADAV400 can also be set up to accept double- or quad-speed

inputs by reducing the number of instructions per sample. This

is set in the audio core control register.

The part is easily programmed using graphical tools provided

by Analog Devices. No knowledge of DSP assembly code is

required to program the ADAV400. Simply connect graphical

blocks, such as biquad filters, dynamics processors, mixers, and

delays, in a signal flow schematic. The schematic is then

compiled, and the program and parameter files are loaded into

the program RAM of the ADAV400 through the control port.

Signal processing blocks available in the provided libraries include

•

Single- and double-precision biquad filters

•

Monochannel and multichannel dynamics processors

•

Mixers and splitters

•

Tone and noise generators

•

First-order filters

•

Fixed and variable gain

•

RMS look-up tables

•

Loudness

•

Delay

•

Stereo enhancement (Phat Stereo™)

•

Dynamic bass boost

•

Interpolators and decimators

Additional blocks are always in development. Analog Devices

also provides proprietary and third-party algorithms for appli-

cations such as matrix decoding, bass enhancement, and surround

virtualizers. Contact Analog Devices for information about

licensing these algorithms.

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