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OmniTek OTR 1001 User Guide, v3.1a
K-6
K.3 Surround Sound
Audio intended for use in a Surround Sound configuration may be analysed either:
As 5.1 or 7.1 ‘Surround Sound’ versions of the audio input that are analysed in the same
way as other audio but with individual channels selected and labelled as L, R, C etc.
according to their intended use (as defined on the Audio Inputs page of the Config
window or, in the case of Dolby audio, as defined by the associated Dolby metadata)
Through special ‘Surround Sound’ displays such as the Surround Sound View described
below that present 5.1 data in a form that is particularly appropriate to the use of the
channels to provide Surround Sound.
The OTR can also display data relating to the Stereo Downmix generated from the Surround
Sound channels following one of the standard formulae – as described below.
Stereo Mix Down
The channels of 5:1 Surround Sound are typically mixed down either to a conventional stereo
pair or to a ‘matrix surround encoded’ stereo pair. The way in which this mixing is done is
specified in the ATSC Digital Audio Compression Standard (AC-3), which defines formulae for
calculating and then scaling the Lo and Ro components of a conventional stereo pair and the Lt
and Rt components of a matrix surround encoded stereo pair from the L, C, R, Ls and Rs
channels, together with formulae for optionally including the LFE channel in the final L and R
stereo pair. The OTR uses the Dolby Prologic version of Lt + Rt, together with a Dolby ProLogic
II-compatible version (referred to here as Lt/Rt II).
A similar approach taken with 7.1 Surround Sound. The only difference is that the Ls used in the
formulae is a 50:50 mix of the Ls and Bsl channels (each reduced by 6dB) while the Rs used in
the formulae is a similar 50:50 mix of the Rs and Bsr channels.
The OTR gives the option of showing Lo/Ro, Lt/Rt or Lt/Rt II alongside L, C, R, Ls and Rs in
displays showing either ‘Surround Sound’ or ‘Dolby’ audio inputs. Information about these
signals also appears in the Status Display, where the derived signals are treated as Channels 17
and 18.
The way in which these signals are determined depends on whether the audio input is embedded,
AES or Dolby.
When working with Embedded or AES audio, the formulae used are:
Lo = L +
cmixlev
* C +
surmixlev
* Ls
(
cmixlev
,
surmixlev
are fields within the bsi data)
Ro = R +
cmixlev
* C +
surmixlev
* Rs
Lt = L + C * (-3dB) – Ls * (-3dB) – Rs * (-3dB)
for ‘Lt/Rt’
Rt = R + C * (-3dB) + Ls * (-3dB) + Rs * (-3dB)
Lt = L + C * (-3dB) – Ls * (-1.2dB) – Rs * (-6.2dB)
for ‘Lt/Rt II’
Rt = R + C * (-3dB) + Ls * (-6.2dB) + Rs * (-1.2dB)
Where the option to include the LFE channel is taken, LFE *
lfemixlev
* (-4.5dB) is added prior
to scaling.
The type of downmix that is shown is selected through the
Stereo Mix Down/Mode
option on
the
Audio Config
page of the Config window.
Summary of Contents for OTR 1001
Page 1: ...Advanced Measurement Technology OTR 1001 User Guide Software Version 3 1 October 2013...
Page 28: ...OmniTek OTR 1001 User Guide v3 1a A 16...
Page 52: ...OmniTek OTR 1001 User Guide v3 1 B 24...
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Page 358: ...OmniTek OTR1001 User Guide v3 1 U 12...
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Page 379: ...OmniTek OTR 1001 User Guide v3 1 I 15 Example XML Statements Example Result...
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