Channel-to-channel loudness control: ALC at head-ends
Channel-to-channel loudness inconsistencies are another key issue, especially for cable and IPTV service providers. It's common for viewers to experience different loudness levels as they switch between channels, and this is because the channels will have different Average Loudness and inconsistent dialnorm values.
Often, the cause of this channel-to-channel loudness variation is the broadcaster's use of a default -27 dB DialNorm value for the Dolby Digital encoder when there is significant variation in the average loudness of the program segments. An example of this type of problem is shown in the diagram below.
Fortunately, Miranda's Automatic Loudness Control solutions can be used to address the problem by decoding and processing the audio with ALC, and then re-encoding (see opposite page). The Densité signal processor card can re-stamp a consistent Dialnorm value to match the target loudness value used by the ALC processor.
Headend uses decoding, ALC audio processing, and re-encoding
Can fix both channel-to-channel and segment-to-segment loudness problemsThis configuration is possible if the audio compression algorithm and the bit rate in use allow for an extra generation of encoding without creating audible artifacts when decoded at final destination
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