Specifications

5.1-Channel Production Guidelines Production Environment
3-13
channels in need of bass management, as determined either by product design or user
selection. The five main channels are then high-pass filtered at either a fixed
frequency of 80 Hz or a selectable frequency of 80, 100, or 120 Hz. The summation
of the LFE and any other channels is low-pass filtered at the same frequency. If the
crossover frequency is fixed at 80 Hz, as is standard in lower priced decoders,
information in the LFE channel between 80 Hz and 120 Hz will be reproduced at a lower
level than it is recorded at. To replicate what the consumer will hear, a third order 80 Hz
filter in the LFE audio signal path to the recorder is recommended.
While the Dolby Digital Encoder and Decoder together will handle bass management
in decoding, it is not feasible to use it in this way when mixing, due to the delay
through the encoding and decoding process. Because of this, it is necessary to have a
separate crossover system in place to handle the bass management. Many
manufacturers now offer such devices for this purpose. Again, for DVD and other
consumer applications, a crossover frequency of 80 Hz is required.
Once the ability to reproduce all frequencies in each channel has been met, the room
must be calibrated. For each of the five main channels, pink noise is adjusted for
85 dB C-weighted slow. Various EQ curves will come into play, depending on room
size and application. If in doubt, additional information is available in the Dolby
Surround Mixing Manual, Technical Guidelines for Theater Applications and other
publications from Dolby Laboratories.
The LFE channel is calibrated such that each 1/3 octave band between 20 and 120 Hz
is 10 dB higher than the equivalent 1/3 octave bands for any of the full-range
speakers, assuming that the full-range speaker is ideally flat. This level is read from a