Dolby Laboratories DP570 - Manual (Page 112)

100 Dolby ® DP570 Multichannel Audio Tool User’s Manual
A Guide to Dolby Metadata Parameter Definitions
it prevents aliasing on decoding and is normally switched on. This parameter is not passed
to the consumer decoder.
LFE Lowpass Filter
This parameter determines whether a 120 Hz eighth‐order lowpass filter is applied to the
LFE channel input of a Dolby Digital encoder prior to encoding. It is ignored if the LFE
channel is disabled. This parameter is not sent to the consumer decoder. The filter removes
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
Table D-17 Lowpass Filter Setting
Lowpass Filter Setting
Enabled
Disabled
Table D-18 LFE Lowpass Filters
LFE Lowpass Filter Setting
Enabled
Disabled
Table D-19 Surround 3 dB Attenuation Settings
Surround 3 dB
Attenuation Setting
Enabled
Disabled