Cirrus Logic CobraNet - Manual (Page 20)

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©
Copyright 2006 Cirrus Logic, Inc. DS651PM25
CobraNet Programmer’s Reference
Audio Paths
the network receivers to the SSI outputs. Routing channel 0 is a special logical channel
used to supply silence to a transmitted channel or serve as a “bit bucket” when receiving
from the network.
Audio arrives and leaves the interface through the SSI receivers and transmitters. As
each sample arrives it is buffered. The mapping of audio input and output channels to
audio I/O buffer offsets is fixed (and non-intuitive). To accommodate channel numbering
differences of different CobraNet devices, the
audioMap variables allow a mapping from
audio I/O buffer offsets to routing channel numbers. This mapping is preset by the
manufacturer and should never need to be altered.
4.2 Bundle Transmitters
A Transmitter is a logical entity within the CobraNet interface capable of transmitting one
bundle of up to 8 audio channels. Input audio routing channels (0, 1 through 32) are
mapped into Bundles associated with a particular transmitter via the
txSubMap variables
associated with that transmitter. There are 8 txSubmap variables associated with each
transmitter, each of which can be set to a particular routing channel number. The first
txSubMap variable sets the routing channel that will be transmitted in the first audio
channel in the bundle. The second
txSubmap variable selects the source for the second
audio channel to be transmitted in the bundle...and so on.
Audio resolution (sample size) and sample rate (48 kHz or 96 kHz) are determined by
other transmitter parameters discussed in this document.
4.3 Bundle Receivers
A Receiver is a logical entity within the CobraNet interface capable of receiving one
bundle of up to 8 audio channels. Output audio routing channels (0, 33 through 64) are
mapped from the receiver via the
rxSubMap variables. There are 8 rxSubMap variables
associated with each receiver, each of which can be set to a particular routing channel
number. The first
rxSubMap variable selects the routing channel that will receive the first
audio channel in the bundle. The second rxSubMap variable specifies mapping the
second audio channel in the bundle...and so on.
4.4 Loopback
The loopback object provides a means for the interface to transfer audio channels
internally. Loopback overcomes the limitation that a device cannot receive its own
transmission and also allows the audio I/O system to be tested locally.
The audioLoopSource and audioLoopDest variables control this feature.
4.5 Output Channel Duplication
The audio routing channel mapping facilities allow a single routing channel to be mapped
to any number of audio channels in any number of network transmitters (Bundles). It is,
however, not possible to direct an audio channel in a network receiver to multiple audio
routing channels for output through multiple SSI channels or ports.
Output channel duplication allows output routing channels to be copied to other output
routing channels. This feature is implemented as a separate set of “dup” paths controlled