Cirrus Logic CobraNet - Manual (Page 21)

CobraNet Programmer’s Reference
Audio Paths
DS651PM25
©
Copyright 2006 Cirrus Logic, Inc. 21
by audioDupSource and audioDupDest variables. An output can be specified as the
source for a duplication by multiple “dup” paths. Output duplication is accomplished
without incurring additional audio latency. See
Section 6.4.10 "Audio" on page 92 for
more information.
4.6 Meters
Metering is provided for all 64 audio routing channels. The first 32 meters can be mapped
to the 32 input routing channels. The second 32 meters are used to meter the output
routing channels. Mapping is controlled by the
audioMeterMap variable
.
Metering is disabled by default to conserve processing cycles. Meters are peak detecting
with simple first-order decay ballistics. Ballistics are comprised of an instantaneous attack
and exponential decay time programmable via
audioMeterDecay variable. Ballistics are
adjusted globally for all meters. All level measurements are peak level (as opposed to
RMS, for instance). Level is indicated in 24-or 32-bit positive signed values. A cumulative
peak hold element on each meter allows accurate detection of any clipping condition. See
Section 6.4.10 "Audio" on page 92 for more information.
4.7 Low-latency Audio Support
Low-latency modes are supported on CobraNet interfaces without need for hardware
changes to the CobraNet interface or CobraNet Device. The default mode of operation is
5-1/3 mS latency at 48 kHz sample rate.
Running in low-latency mode requires more processing power, implying a trade-off
between the number of channels supported and reduction of latency. Some reference-
design-based products need to operate at reduced channel count to support lower
latency. Depending on selected sample size, sample rate, and latency, newer CobraNet
interfaces may be subject to some limitation in channel capacity, number of transmitters
and receivers, and multiple unicast transmission count.
The following table shows CM-1 channel capacity for several latency and sample rate
operating modes. Eight-channel bundles with 20-bit resolution, unicast to a single
destination or multicast is assumed.
Low-latency modes also place additional demands on network performance. Specifically,
in order to achieve the desired latency, forwarding delay across the network needs to be
reduced by approximately the same factor that audio latency is reduced. These
requirements bring into play new network design rules.
Lower latency is achieved by transmitting smaller audio packets at a higher rate. A
restriction on the number of audio channels allowed in a bundle is due to a restriction on