GatesAir PTR-255 Program Audio Codec Module
Intraplex Products Issue 2.1, February 2006
The audio input feeds a 24-bit linear analog to digital converter with 128x oversampling. The
sample rate is user-selectable and can be either 16 ksps, 24 ksps, 32 ksps or 48 ksps. When using
MPEG Layer 2, only 32 ksps or 48 ksps are available.
On the output side, 20 bit linear data is converted by a digital to analog converter. The output
impedance is balanced, less than 100 .
2.2.1 Programmable Gain
The input sensitivity (overload level) for each analog input channel is adjustable in 1dB steps
from +9dBu to +24dBu, with a step accuracy of 0.2dB. The factory default setting is +20dBu.
This setting allows a peak input signal of +20dBu to produce digital full scale, providing proper
headroom for most audio applications.
A similar adjustment range is provided for the analog output gain.
The level adjustment potentiometers are on the front edge of the card. When the card is set for
remote control, level adjustments can be made using the IntraGuide™ user interface software.
2.3 Digital Audio
The digital audio input is an AES/EBU interface that accepts either 32, 44.1 or 48 ksps sample
rates.
The PTR-255 transmits only the audio bits from the AES/EBU data stream and reconstructs the
AES/EBU header at the output. The output sample rate is user-selectable for either 32 or 48 ksps
and the audio output format is user-selectable for professional. For consumer format, the output
sample rate is 48 ksps.
The AES output signal may be synchronized to either an internal or an external clock signal. In
this context, the internal clock is that being used by the multiplexer and the external clock is
recovered from the AES/EBU input. This is a user-selectable feature. If external clock is selected
but the card cannot recover a sync signal from the incoming AES/EBU data stream, it will default
to using its internal clock and fall back to the analog input.
2.3.1 AES/EBU Channel Status
The AES/EBU data format includes channel status information on the audio signal being
transported. This channel status information may be structured in either consumer format or
professional format, as described in the following sections. The PTR-255 modules support
both formats. In AES/EBU terminology, “A channel” refers to the left audio channel and “B
channel” refers to the right audio channel.
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