Clicks and Pops in DTV Audio, Part Two - TvTechnology

Clicks and Pops in DTV Audio, Part Two

Are viewers complaining about audio pops and clicks at program transitions? Assuming that Part One, presented last week, solved any timing issues between the external Dolby Digital (AC-3) audio encoder and the DTV video encoder and multiplexer, the focus of this tip will shift to a mode change inside of the audio encod
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Are viewers complaining about audio pops and clicks at program transitions? Assuming that Part One, presented last week, solved any timing issues between the external Dolby Digital (AC-3) audio encoder and the DTV video encoder and multiplexer, the focus of this tip will shift to a mode change inside of the audio encoder itself.

The audio bitstream can be encoded for the number of audio channels present and this is represented by the Audio Coding Mode (acmod) metadata parameter. For example, if a 5.1 channel program is presented to the encoder, Audio Coding Mode should be configured to 3/2L, while a two-channel program would be encoded as 2/0. This simple notation, front channels/rear channels/LFE (i.e. subwoofer channel) can be seen on the front panel display of the encoder and will directly affect how consumer equipment decodes the audio.

There are two common ways to change this mode on the encoder. The first and best way is by changing the metadata parameter. This, by far, is the cleanest way to do it, but it is not the most simple as it may require external equipment, and it also will not eradicate the problem completely. The other way to make this change is by setting up GPI control to switch between two presets: a 5.1 channel (3/2L) preset and a two-channel (2/0) preset. Pressing the front panel preset switches can also recall a preset. Unfortunately, the preset method does not always produce the cleanest sounding result for a variety of reasons.

The major problem lies in some 5.2 channel consumer receivers that exhibit a small hiccup when this mode changes. While the issue has been noted and corrected, many receivers exist that do have the problem. One solution might be to make all audio 5.1 channels all the time by using techniques such as upmixing. This removes the need to ever change Audio Coding Mode, thereby eliminating the problem.