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Audio track layouts

Which track carries what.

The broadcast track allocations in one place: the EBU R123 file-exchange layouts and R48 tape-era cases that delivery specs cite by number, the 5.1 channel-order trap, and where Dolby E sits.

5.1 channel order: broadcast vs film

The single most common re-mapping mistake: the two conventions agree on channel 1 only.

SMPTE broadcast order (EBU R123 / R48)
L
R
C
LFE
Ls
Rs
Film / Pro Tools convention
L
C
R
Ls
Rs
LFE

Red cells differ from the broadcast order. EBU R123/R48 (and broadcast delivery generally) use L R C LFE Ls Rs; the film order is the common film/Pro Tools convention.

Track allocations

Programme mixDiscrete 5.1 (MCA)Encoded MCA (e.g. Dolby E)International sound / M&E / FXAudio description / foreign languageMonoM/S + Ambisonic B-format
R123: 2aEncoded MCA only
1
enc MCA
2
enc MCA
R123: 4aStereo with encoded MCA
1
Ⓢ L
2
Ⓢ R
3
enc MCA
4
enc MCA
R123: 4bStereo with IT or EFXused by ARD, ZDF, ORF
1
Ⓢ Mix L
2
Ⓢ Mix R
3
IT/EFX L
4
IT/EFX R
R123: 4cStereo with AD or FLused by ARD, ZDF, ORF
1
Ⓢ L
2
Ⓢ R
3
AD/FL L
4
AD/FL R
R123: 8aStereo with discrete MCA
1
Ⓢ L
2
Ⓢ R
3
MCA L
4
MCA R
5
MCA C
6
MCA LFE
7
MCA Ls
8
MCA Rs
R123: 8bDiscrete MCA with stereo
1
MCA L
2
MCA R
3
MCA C
4
MCA LFE
5
MCA Ls
6
MCA Rs
7
Ⓢ L
8
Ⓢ R
R123: 8cDiscrete MCA with 2 × mono
1
MCA L
2
MCA R
3
MCA C
4
MCA LFE
5
MCA Ls
6
MCA Rs
7
Ⓜ
8
Ⓜ
R123: 8d2 × stereo with 2 × encoded MCAused by Sky
1
Ⓢ Mix L
2
Ⓢ Mix R
3
Ⓢ EFX L
4
Ⓢ EFX R
5
enc MCA Mix
6
enc MCA Mix
7
enc MCA EFX
8
enc MCA EFX
R123: 8e2 × stereo with 2 × encoded MCA (variant)
1
Ⓢ Mix L
2
Ⓢ Mix R
3
enc MCA Mix
4
enc MCA Mix
5
Ⓢ EFX L
6
Ⓢ EFX R
7
enc MCA EFX
8
enc MCA EFX
R123: 8fStereo with M/S and/or B-format Ambisonics
1
Ⓢ L
2
Ⓢ R
3
ⓈM
4
ⓈS
5
W
6
X
7
Y
8
Z
R123: 8gStereo with AD/FL, IT and encoded MCAused by ARD, ZDF, ORF
1
Ⓢ Mix L
2
Ⓢ Mix R
3
AD/FL L
4
AD/FL R
5
IT L
6
IT R
7
enc MCA
8
enc MCA
R123: 8hStereo with encoded MCA, IT and AD/FLused by ARD, ZDF, ORF
1
Ⓢ Mix L
2
Ⓢ Mix R
3
enc MCA Mix
4
enc MCA Mix
5
IT L
6
IT R
7
AD/FL L
8
AD/FL R
R123: 8iStereo with IT/M&E, IT and encoded MCAused by ARD, ZDF, ORF
1
Ⓢ Mix L
2
Ⓢ Mix R
3
IT/ME L
4
IT/ME R
5
IT L
6
IT R
7
enc MCA Mix
8
enc MCA Mix

R123 Table 1 also defines 12- and 16-track families (multi-language, sport main/clean-effects splits) along the same patterns. Audio for file exchange should be 48 kHz, 24-bit, time-aligned with picture.

Broadcaster examples

From current delivery specifications. Always confirm against the commissioning spec for your delivery.

ITV (HD)

R48: 2a · R123: 4b

4 or 16 channels; stereo only (5.1 not supported for ITV HD). Accepted layouts: R48:2a (stereo on 1–2) or R123:4b (final mix 1–2, M&E 3–4). Unused tracks: PCM silence. No SMPTE ST 2020 Dolby metadata track.

RTÉ (HD)

R123

Up to 8 tracks: 1–2 programme stereo; 3–4 optional M&E or Dolby E; 5–6 optional Audio Description premixed with programme. Unused tracks carry silence. Follows EBU R123.

ZDF (HD)

R123-style allocation

Even track counts 2–16: 1–2 Send L/R; 3–4 second language; 5–6 Audio Description; 7–8 Dolby E; 9–14 discrete 5.1 (L R C LFE Ls Rs); 15–16 by agreement.

Dolby E in two sentences

Dolby E packs a multichannel mix into what looks like a stereo PCM pair (6 channels at 16-bit, 8at 20-bit), so a 5.1 mix can ride on two tracks of an 8- or 16-track master (in R123 layouts it appears as the “encoded MCA” pairs). It is data, not audio: play it as PCM and you get full-scale noise, which is why delivery specs are explicit about which tracks may carry it and why unused tracks must be true silence.

Why layouts are cited by number

Specs say “R48:2a” or “R123:4b” instead of prose because the allocation must be unambiguous for international exchange, the whole point of both recommendations. If a QC report flags your audio configuration, the fix is almost always moving content to the tracks the cited layout expects, not re-mixing.

SpectraQC checks track counts, channel maps, silence on unused tracks, and loudness per delivery spec: see the audio checks.