Service manual

DSP SYSTEM

A simplified block diagram of the DSP system is shown on the next page. At the heart of

the system is an Analog Devices ADSP-2181. It acts as the console CPU, and controls all

functions and communications within the DSP system. There are 24 proprietary DSP chips

to handle the actual audio processing. Parallel processing with the 24 DSPs allows the

d8b to complete all processing within one sample.

Operating instructions are loaded from the Remote CPU as the system boots. The

EPROM does not contain operating firmware. Think of the EPROM as BIOS, it provides the

system with basic instructions to make sure it powers up correctly and sets up to receive

the operating software from the Remote CPU.

CLOCKS

All audio clocks for the DSP system originate at the clock (sync) card. The master clock is

512 x sample rate. See page 24 for some more details.

CODEC BOARD

The CODEC board contains 24 channels of A/D and D/A. Each ADC converts two

analog audio signals into a two channel serial format which is sent to the DSP chips. All

digital audio signals within the d8b are in this two channel format. The DACs convert this

stream back to 2 channels of lovely analog audio.

DSP BOARD

Each of the 24 DSP chips has two serial inputs, DR_0 and DR_1, and two serial outputs,

DT_0 and DT_1, a total of 48 inputs and 48 outputs (remember that each serial input is 2

channels of audio, so that’s 96 channels!, but they’re not all used). Digital audio data

comes from and is sent to the CODEC board, I/O cards, and FX cards.

Y2 is the processor clock from which is derived CLK_1, CLK_2, CLK_3, CLK_4 and CLKIN.

Y1 is a UART clock.

DSP INPUTS DSP OUTPUTS

12 Mic/Line Inputs 8 Subgroups

12 Line Inputs 2 L/R Mix

24 Tape Input Cards 24 Tape Returns Cards

16 FX Card Returns 16 FX Card Sends

2 Meter (monitor) 12 Aux sends

8 Alt Input Card 8 Alt Output Card

2 Solo

The processing algorithm works in such a way that each serial output consists of one

mix and one direct output. In order to route mixes to the same DACs the serial data is

juxtaposed in sync with the L/R clock.

There are three status indicators on the board: D2 (green),D3 (yellow), D1 (red).

•If all three are on, a fault has been detected.

•If the red LED is on solidly, then this is operating OK.