Cisco D9054 Installation And Operation Manual page 159

Setting Up AAC Processing,
3. Select the Bit Stream Mode.
Use this field to select the format of the bit stream. This is used by the decoding
system and does not affect the performance of the actual signal.
You may select MPEG-2 ADTS (Audio Data Transport Stream), MPEG-4 ADTS,
MPEG-4 LOAS (Low Overhead Audio Stream), or MPEG-4 LATM LOAS
Explicit (available for encoders equipped with a Multiple Channel Audio
(MCA) card only).
ADTS is the primary ES format used for MPEG-2 AAC-LC but is also the most
common format in MPEG-4 AAC-LC and AAC-HE broadcast applications. The
difference between MPEG-2 and MPEG-4 ADTS headers is a single bit, which
indicates to the decoder which compression "tools" may have been used in
creating the ADTS payload. For MPEG-2 streams, this is Temporal Noise
Shaping (TNS) and Mid-Side Encoding (MS). MPEG-4 provides additional tools
such as Spectral Band Replication (SBR) and Perceptual Noise Substitution
(PNS). Most MPEG-2 decoders will mute the audio output when a MPEG-4
stream is indicated since they will not recognize streams created with SBR or
PNS tools. MPEG-4 LOAS is mainly used for audio only (no video) services.
Selection will be based on the requirements of the target decoders. MPEG-4
ADTS is only valid for bit rates below 128 kbit/s.
4. Enable the relevant compression tools. The functions of the various tools are as
follows:
Tool
Temporal Noise
Shaping (TNS)
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Continued
Function
The basic idea of TNS relies on the duality of time
and frequency domain. TNS uses a prediction
approach in the frequency domain to shape the
quantization noise over time. It applies a filter to the
original spectrum and quantizes this filtered signal.
Additionally, quantized filter coefficients are
transmitted in the bit stream. These are used in the
decoder to undo the filtering performed in the
encoder, leading to a temporally shaped distribution
of quantization noise in the decoded audio signal.
(This means the noise can appear shortly after or
even before the exciter signal, so it's an intentional
"post/pre-echo", but not noticeable if implemented
correctly, i.e., below the masking threshold.)
D9054 HDTV Encoder Intstallation and Operation Guide 5-75