[BC] DTV Audio Levels

[Clayborn, Kevin]

Hi Richard,

I believe you are missing the mark here. The complaint, and the problem,
isn't just a simple level problem. It has more to do with audio density
of the received content from production houses.

Some factors regarding apparent audio volume of commercials has a lot to
do with the following: (from the expert, Bob Orban)

The four most important factors that correlate to the subjective
loudness of broadcasts are these: 

1. The power of the sound.

2. The spectral distribution of the power. The ear's sensitivity depends
strongly on frequency. It is most sensitive to frequencies between 2 and
8 kHz. Sensitivity falls off fastest below 200 Hz. 

3. Whether the power is concentrated in a wide or narrow bandwidth. For
a given total sound power, the sound becomes louder as the power is
spread over a larger number of critical bands (about 1/3 octave). This
is called loudness summation. 

4. Temporal integration: As its duration increases, a sound at a given
level appears progressively louder until its duration exceeds about 200
milliseconds, at which point no further loudness increase occurs.

**

And then the crux of the matter:

Regarding the loudness of commercials: There are two principal
techniques used to make commercials louder than the surrounding program.
The first is dynamic range compression, which increases the average
power. The second is emphasis on frequencies to which the ear is most
sensitive - the region between 1 and 5 kHz.

**

All is not lost however. There are techniques that can help the
broadcaster. Again, from Bob:

Competent loudness meters and automatic loudness controllers (like the
CBS controllers Orban uses in TV Optimods) indirectly take both of these
into account by modeling the four loudness-determining factors listed
above. The CBS LC accurately estimates the amount of perceived loudness
in a given piece of program material. If the loudness exceeds a preset
threshold, the controller automatically reduces it to that threshold.
The CBS algorithm has proven its effectiveness by processing millions of
hours of on-air programming and greatly reducing viewer complaints.

When a loud commercial comes along, the CBS LC reduces the gain prior to
the station's final limiter, sometimes to the point where the peak
modulation is well below 100%. Therefore, the station can compensate for
whatever the production house originally did in making a commercial
loud. Even though the commercial's dynamic range remains highly
compressed, its average modulation is reduced to the point where its
loudness is well balanced with other program elements.

Hope this helps explain the problem broadcasters face and some of the
solutions offered to help overcome those problems and reduce audience
irritants and thus complaints.

Regards,

Kevin Clayborn

-----Original Message-----
If I am a network TV station licensee and I get a digital network feed,
can't I control all aspects of that network signal? As the licensee, I
am required to have absolute control. ...snip...If the TV station has
complete control of the content as required by law, then it should be
trivial to maintain audio levels within acceptable limits. Now, if the
network saw fit to multiplex the audio onto the video instead of sending
it by land-line (seems reasonable), then the broadcaster has no choice
but to demultiplex that audio, feed it into something that can control
it, and then multiplex it back. 

Richard B. Johnson