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- Front-end AGC gently rides gain
- Programmable parametric midrange and high-frequency equalizers can be adjusted to complement program material
- Shelving bass equalizer with 12 or 18dB/octave slopes adds punch to music
- Two-band compressor with Loudness Controller retains frequency balance of input program material while limiting subjective loudness to a preset threshold
- Five-band compressor automatically re-equalizes program material to create a consistent sound from poorly produced program material
- Look-ahead peak limiter tightly controls peaks without clipping
- Non-clipping peak limiting produces narrowband modulation products that minimize the strain on the AC3 or MPEG perceptual encoder, maximizing audio quality for a given bit rate.
Why Do We Need Additional Audio Processing With DTV?
- People with home theater systems may leave DRC defeated on their receivers. This means that the program material must be consistently listeNABle without the benefit of the compression built into DRC.
- If no additional processing is used, every piece of program material must be carefully adjusted for level and have a Dialog Normalization value assigned to it manually.
- Loud commercials are by far the greatest source of viewer complaints about TV audio. Without automatic loudness control, viewers are likely to be annoyed by loud commercials-particularly if they have DRC defeated on their receivers.
- Even if viewers take advantage of Dynamic Range Control, DRC is a wideband process that is not aware of subjective loudness, so it can be fooled by highly processed source material, like loud commercials.
- Because DRC is wideband, it cannot automatically re-equalize substandard program material, like live news actualities or old syndicated programs with dated sound quality. Manual gain riding of live material is subject to operator error because operator reaction time is greater than the time required for the ear to perceive a level imbalance.
A Possible Operational Scenario
Some program material should be broadcast with full dynamic range. Some examples include:
- Modern feature films
- Prime-time dramatic programs mixed specifically for DTV
- Some sports with highly produced sound
- Classical music
But other program material does not need wide dynamic range and can be safely applied to audio processing:
- Live news
- Talk shows
- Game shows
- Situation comedies
- Older syndicated programming
- Older and non-stereo feature films
- Pop music
- Sports without highly produced sound
- Commercials and infomercials
Setting Up System
- Set up two parallel paths
- One passes through 5.1 channel material without processing
- The other receives two-channel material requiring processing and applies this material to the 6200.
- The 6200 is set up for one frame of delay.
- The 6200 accepts house sync through its AES/EBU sync input
- Apply the outputs of the two parallel paths to an AES/EBU switcher.
- Set up the Dolby AC-3 encoder with at least three separate presets
- One accepts processed two-channel material
- One accepts unprocessed two-channel material and has a one-frame delay by comparison to (1)
- One accepts unprocessed 5.1-channel material and has a one-frame delay by comparison to (1)
- When (2) and (3) are active, the system passes along DRC data from the producer of the material.
- DIALNORM may have to be set locally to ensure loudness consistency
Benefits
The home theater owner can enjoy well-mixed 5.1 channel material with full dynamic range, yet is protected from excessively loud commercials and annoying loudness inconsistencies in "garden variety" program material The owner of a mass-market receiver can enjoy comfortably listeNABle sound as he or she now does with well-processed NTSC, PAL, or SECAM transmissions The 6200's automatic level and loudness control minimizes the broadcaster's labor burden and prevents operational errors on all material passed through the 6200.