LFE and Rear Channel decoding with APT-x100 plugin

[schorman]

Hello, I've started working with your APT-x100 decoder, and it works really well. Since the codec encodes the LFE channel as part of the two surround channels, I was wondering if you could describe how the LFE and surround channels are decoded by your plugin.

What sort of High pass/Low pass filtering is done to separate out the different channels?

Are the calculations done at 32bit, 24bit, or 16bit?

Thanks for your extremely useful tool!

[Maxim V.Anisiutkin]

Plugin uses 4-th order LF IIR filter with 80 Hz cutoff to extract LFE channel from L/R surround channels: LFE = (LF_filter(Ls) + LF_filter(Rs)) / 2. And the dual filter (4-th order HF IIR, 80 Hz cutoff) removes LFE data from L/R surround channels.

LF/HF filters use double format (64 bit floating point). Then results are dithered and rounded to 16 bit.

[schorman]

Thanks for the explanation. It's really nice to have this all integrated within the plugin.