Apple Soundtrack Pro 3 - Manual (Page 441)

• Data Rate pop-up menu: The choices depend on the coding mode and target system.
The higher the rate, the better the quality. Dolby Digital Professional (AC-3) streams
have a constant data rate. At 448 kbps, which is the default for 5.1 encoding, one minute
of AC-3 audio takes about 3.3 MB of storage space. For stereo encoding, rates of 192 kbps
and 224 kbps are typical and will produce good results.
• Bit Stream Mode pop-up menu: Defines the purpose of the encoded audio material. The
information is included in the finished stream and can be read by some decoding
systems.
• Dialog Normalization field: Specifies the average volume of the dialogue, using decibels
of full scale (dBFS), in your sound files relative to full modulation. The playback device
uses this information to maintain similar volume among different AC-3 streams. The
goal is to make all AC-3 encoded audio files have the same listening level, regardless
of the source file.
It is especially important to properly use the Dialog Normalization feature if you have
different audio files (with different volume levels) going on to a DVD. If you know the
average level for each of them, enter that number in the Dialog Normalization field for
each file. For example, if the dialogue in your project averages around –12 dB on the
level meter, enter –12 in the Dialog Normalization field.
Note: This normalization is between the audio streams on the DVD, not within an
individual audio stream itself.
You can enter values from –1 dBFS to –31 dBFS. The louder the source file, the smaller
the value you enter, and the more the audio in the encoded file is attenuated during
playback.
The difference between the value you enter and 31 dBFS (which represents the normal
dialogue listening level) is the amount that the source audio is attenuated. For example:
• If you enter –31 dBFS: The attenuation is 0 dB (31 dBFS–31 dBFS), and the source
audio levels are not affected at all.
• If you enter –27 dBFS: The attenuation is 4 dB (31 dBFS–27 dBFS).
• If you enter –12 dBFS: The attenuation is 19 dB (31 dBFS–12 dBFS).
Important: It is critical that you have set the Dialog Normalization setting correctly if
you intend to use any of the Compression Preset settings. The Compression Preset
settings assume that the audio, after the dialogue has been normalized, is at the normal
listening level of 31 dBFS. Levels that are consistently louder than that result in distorted
sound and erratic levels.
If you want to ensure that the AC-3 encoder does not affect your sound levels, enter
–31 for the Dialog Normalization and choose None from the Compression Preset pop-up
menu (located in the Preprocessing pane).
441 Chapter 20 Exporting Multitrack Projects