Audio Specifications

Audio processing chain

The audio processing chain is composed of the following elements:

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One audio input front-end including one analog two digital embedded audio sources and oe audio multiplexer

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One sample rate converter

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Three encoders

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One set of audio outputs

Audio inputs front-end

The audio multiplexer selects a digital audio stream from one of the following three audio sources:

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Analog audio source

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SDI audio source

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HDMI audio source

The analog audio interface digitizes the analog audio stereo signal at 48 kHz.

The HDMI and SDI interfaces extract up to two audio channels of the embedded audio/video signal. The sampling rate for such audio signal is determined by the HDMI/HD-SDI source.

Sampling rate converter

The sample rate converter adapts the sample rate of the audio stream to the desired rate.

The sample rate is defined once for all the encoded audio streams and the audio outputs. If e.g. we want to use G.711 encoder (8kHz), simultaneous output as linear PCM or AAC is only possible at 8kHz!

Audio encoders

There are 3 audio encoders: one G.7xx encoder, one AAC encoder and one Linear PCM encoder.

Up to 3 encoders can be used providing that they are requiring the same sampling rate. This is tested and enforced by the web service layer, that will not allow simultaneous use of two encoders requiring conflicting sampling rates.

Important side-effect: producing G.711 out of de-embedded audio might thus be available only when embedded audio is sampled by the source at 8kHz.

Audio outputs set

The audio stream can feed:

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Two digital audio channels of the HDMI Output

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Left and Right channels of the analog audio output through a stereo DAC converter.