ScoopTeam - User manual - Draft 0002
11
MPEG Audio Layer 2 coding
Application: mono or stereo music, high quality.
As shown on Table 2, this coding algorithm features a maximum flexibility, with many variations for bit
rate, mono or dual mono channel mode, sampling rates...
The 24 kHz sampling rate (
NYA
) features a moderate bandwidth (10 kHz) and is rather useful for
commentaries.
The latency is rather high with this sampling rates
ISDN mode specific aspects: J52 (
NYA
)
For ISDN transmission, MPEG L2 is proposed with two variations:
“MPEG L2 J52” variation (
NYA
), using the ITU-T J52 protocol for the link negotiation and inverse
multiplexing (B channel aggregation for connections requiring more than 64 kbit/s). For more
details refer to 2.3.2, ISDN interface (page 14).
“MPEG L2” variation, without the J52 protocol. At 128 kbit/s, this variation uses a system for
inverse multiplexing two B channels that is proprietary but compatible with several codecs on
the market.
MPEG AAC algorithms
Application: music, low capacity transmission channels.
These algorithms feature a very high compression ratio, for a given audio quality, compared to Layer 2.
They operate at a sampling rate of 48 kHz, and several bit rates: 16, 20, 24, 32, 40, 48, 56, 64, 96, 128,
192, 256 kbit/s. Two coding variations are available:
MPEG
AAC-LC
(“Low Complexity”): lower compression than HE-AAC, but lower latency.
MPEG
HE-AAC
(“High Efficiency” AAC): higher compression, and the bit rate is limited to
128 kbit/s for this variation.
OPUS coding
Application
music, low capacity transmission channels. Moderate latency.
Opus is an open source coding algorithm (under BSD license), described by RFC6716 from the IETF. Like
MPEG coding algorithms, it is a wide band audio codec, but it features distinctive characteristics:
Low latency; the algorithmic delay of Opus is very low compared to MPEG coding (Layer 2, AAC,
HE-AAC...).
Adaptability: Opus features many parameters influencing its performance, but it is possible to
adapt them automatically depending on the external constraints and the signal characteristics.
In the ScoopTeam, the configuration stays very simple: the user just imposes the desired bit
rate, and the codec automatically adjusts the other parameters (for instance the audio
bandwidth).
Capacity to apply changes “on the fly”: the coding allows changing its operation parameters on
the fly, with no interruption and no artefacts when switching. In this way the bit rate can be
changed during the link on the ScoopTeam, without any audio noise or dropout.
In addition, when the remote device is another AETA codec, it will automatically apply the same
bit rate change to the stream it is transmitting.
Opus coding is only available for IP networks (wired or mobile).
