Ensemble Designs 9670 Audio Automatic Gain and Loudness Control and 9690 Audio Compliance and Monitoring Software - Manual (Page 25)

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Avenue 9670 - page 25
LevelTrack™ Audio Loudness Control AGC Software Option
the most commonly used format throughout the world, either as PAL or NTSC. It is also referred to as
Encoded video.
Color Difference
Color Difference systems take advantage of the details of human vision. We have more acuity in our
black and white vision than we do in color. This means that we need only the luminance information to
be carried at full bandwidth, we can scrimp on the color channels. In order to do this, RGB information
is converted to carry all of the luminance (Y is the black and white of the scene) in a single channel.
The other two channels are used to carry the “color difference”. Noted as B-Y and R-Y, these two signals
describe how a particular pixel “differs” from being purely black and white. These channels typically
have only half the bandwidth of the luminance.
Decibel (dB)
The decibel is a unit of measure used to express the ratio in the amplitude or power of two signals. A
difference of 20 dB corresponds to a 10:1 ratio between two signals, 6 dB is approximately a 2:1 ration.
Decibels add while the ratios multiply, so 26 dB is a 20:1 ratio, and 14 dB is a 5:1 ratio. There are several
special cases of the dB scale, where the reference is implied. Thus, dBm refers to power relative to 1
milliwatt, and dBu refers to voltage relative to .775V RMS. The original unit of measure was the Bel
(10 times bigger), named after Alexander Graham Bell.
dBFS
In Digital Audio systems, the largest numerical value that can be represented is referred to as Full
Scale. No values or audio levels greater than FS can be reproduced because they would be clipped.
The nominal operating point (roughly corresponding to 0 VU) must be set below FS in order to have
headroom for audio peaks. This operating point is described relative to FS, so a digital reference level
of -20 dBFS has 20 dB of headroom before hitting the FS clipping point.
DVI
Digital Visual Interface. DVI-I (integrated) provides both digital and analog connectivity. The larger
group of pins on the connector are digital while the four pins on the right are analog.
EDH
Error Detection and Handling is a method to verify proper reception of an SDI or HD-SDI signal at the
destination. The originating device inserts a data packet in the vertical interval of the SDI signal and
every line of the HD signal which contains a checksum of the entire video frame. This checksum is
formed by adding up the numerical values of all of the samples in the frame, using a complex formula.
At the destination this same formula is applied to the incoming video and the resulting value is
compared to the one included in the transmission. If they match, then the content has all arrived with
no errors. If they don’t, then an error has occurred.
Embedded Audio
Digital Audio can be carried along in the same bitstream as an SDI or HD-SDI signal by taking
advantage of the gaps in the transmission which correspond to the horizontal and vertical intervals
of the television waveform. This technique can be very cost effective in transmission and routing, but
can also add complexity to signal handling issues because the audio content can no longer be treated
independently of the video.