Innes Corporation Pty Ltd
3/38 Leighton Pl
Hornsby, NSW 2077, Australia
Phone: +61 2 9987 0499
Fax: +61 2 9987 0599
E-mail:
Website: http://www.innescorp.com.au
11
DigiTorc M Manual
Functional Description
The AES3 inputs are decoded and sample-rate converted to the output-sampling rate by the
CS8420 transceivers, which also generate the AES3 outputs directly from the outputs of the
digital signal processor. A CS8427 is used for the AES11 synchronisation receiver.
Digitized audio is passed in serial form between the transceivers and the Analog Devices
ADSP21161 digital signal processor. The DSP provides a circular buffer as short term FIFO
storage to cover latency times between PCI transfers, and also performs the software sampling
rate conversion, level adjustment and mixing functions. Host-initiated bus mastering is used for
audio data transfer through the PLX PCI9054 PCI interface.
Configuration data for the PCI interface is stored in a serial EEPROM, which is programmed in
the factory during initial setup of the board.
The DSP software is uploaded from the PC whenever the DigiTorc device driver is started. The
DigiTorc supports standby and hibernation power management modes.
A separately regulated analog 5V plane is used for the AES3 and AES11 input phase-locked-
loops in order to minimise any digital noise on the recovered clock signals.
On playback, the audio stream from the Windows application is first converted to 32-bit stereo
by the Windows kernel mixer and then passed to the DSP where it is rate-converted to the
hardware output sampling rate and mixed with the other output sources.
On record, the audio stream is firstly rate-converted to the hardware output sampling rate using
the sampling rate converter in the CS8420 transceiver, and is then converted again to the
requested software rate and bit depth by the DSP before being passed to the Windows
application.
On both record and playback, if the software sampling rate is equal to the hardware output rate
the DSP’s sampling rate conversion is bypassed.
