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Modern AVR Topology

A lot of discussion in the hobbiest forums on the correct implementation of AVR firmware after it was discovered that the maker of my AVR might have completely botched the implementation of their mixer software, the result being that equalizers end up being applied to the wrong channels and that some channels are set to the wrong volume level or sometimes don't even work.

In order to track the discussion I charted out a possible topology for an AVR. To me this format makes the most sense, but I ddi not consult any resources for this, just relied on my own experience and knowledge. I also skipped the video processing section as it is not relevant (and not to mention under developed in almost every AVR, most tend to pass video through the best you can hope for is that they don't introduce error or scrape information which is very common).

BluRay Player
The focus is not the source here, it could be any source. But HDMI audio tends to be some kind of PCM or minimally encoded digital audio signal.

Bass Management
Bass management applies crossovers to the source material to prepare for future processing.

Mixer
The mixer takes the speaker configuration, the source channels audio (bass management applied) and the mixer setting (e.g. stereo only, upmixing to surround sound, downsampling a 7.1 channel source to 5.1, etc) and mixes them to the appropriate output channels and then has the task of properly level matching all the channels correctly.

Level Trimming
An old skool, but still apparently popular "knob" that allows you to manually boost/degrade bass or treble.

DRC
Digital Room Correction. For example DIRAC automatically measures and calculates amplitude and delay to ensure signals from all channels are time aligned. DIRAC also provides amplitude correction over frequency to remove modes and finally provides cancellation for 1st order reflections in the room.

Analog Sections
Again not the focus of this article, but the DAC, amplifier and speakers are the final and critical output section of any AVR.

Summary
The total number of permutations possible in any typical home theater crossed with the number of codecs and different sources out there is daunting. I don't forgive my AVR vendor for such amateurish efforts but I do understand them.

<source codecs> x <source channels> x <processor settings> x <output speakers>

And this is just the beginning. Vendors must also contend with the following:

  • Turning features on and off without causing drop outs or glitches (e.g. no audio, wrong settings, noise, loud bursts, etc)
  • Preamp switching also must not cause dropouts or glitches
  • A codec is not a codec, there are a number of different encoders and studios all with their own preferences or quirks

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