Within the ATSC DTV audio specification (A/52), a metadata parameter called "dialog loudness" or "dialnorm" is described. This parameter very simply controls a non-defeatable 1 dB per step attenuator present in all consumer receivers and decoders. In its simplest terms, it is a volume control behind the consumer's normal volume control, and it is adjusted by the broadcaster. The parameter has a 30 dB range, and is intended to indicate the average loudness of average dialog in a given program.
Assuming that all programs are measured correctly using the specified LeqA meter (or equivalent) and this dialog loudness value is set to match the measurement, then the average loudness of each program will match. If this is done for every program, on every channel (local and network) then program-to-program loudness will be consistent, as will channel-to-channel loudness. The caveat is that if one program is measured wrong, set wrong, or not set at all, then loudness shifts will almost surely be the result.
With everything that a local station already has to do, is there truly time to measure and set all incoming programming? There are indeed additional options available that work with the dialog loudness parameter to accomplish the same goal of matching loudness.
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