Dolby Laboratories Multichannel Audio Tool DP570 - Manual (Page 115)

Extended Bitstream Information Parameters
Dolby ® DP570 Multichannel Audio Tool User’s Manual 99
frequencies above 120 Hz that would cause aliasing when decoded. This filter should only
be switched off if the audio to be encoded is known to have no signal above 120 Hz.
Surround 3 dB Attenuation
The Surround 3 dB Attenuation parameter determines whether the surround channel(s)
are attenuated 3 dB before encoding. The attenuation actually takes place inside the Dolby
Digital encoder. It balances the signal levels between theatrical mixing rooms (dubbing
stages) and consumer mixing rooms (DVD or TV studios). Consumer mixing rooms are
calibrated so that all five main channels are at the same sound pressure level (SPL). To
maintain compatibility with older film formats, theatrical mixing rooms calibrate the SPL
of the surround channels 3 dB lower than the front channels. The consequence is that signal
levels on tape are 3 dB louder. Therefore, to convert from a theatrical calibration to a
consumer mix, it is necessary to reduce the surround levels by 3 dB by enabling this
parameter.
Surround Phase Shift
The default setting is Enabled , which causes the Dolby Digital encoder to apply a 90‐degree
phase shift to the Surround channels. This allows a Dolby Digital decoder to create an Lt/Rt
downmix simply. For most material, the phase shift has a minimal impact when the Dolby
Digital program is decoded to 5.1 channels, but it provides an Lt/Rt output that can be
decoded with Pro Logic to L, C, R, and S, if desired.
Otherwise, we recommend that you leave this parameter enabled for normal program
material to avoid problems with the analog outputs of set‐top boxes.
D.7 Extended Bitstream Information Parameters
In response to requests from content producers, Dolby Laboratories modified the
definitions of several metadata parameters from their original definition as described in
Table D-18 LFE Lowpass Filter Settings
LFE Lowpass Filter
Enabled
Disabled
Table D-19 Surround 3 dB Attenuation Settings
Surround 3 dB
Attenuation
Enabled
Disabled
Note: This parameter should always be turned off when you are working with steady
state tones for testing purposes (for example calibration discs).
Table D-20 Surround Phase Shift Settings
Surround Phase Shift
Enabled
Disabled