Quickly about AC2

I’ve finally had a look at this codec and it’s not particularly remarkable (and I did it mostly because it beats documenting minute details of MVS). Anyway, there’s nothing much interesting about it. Like its successor, it employs parametric bit allocation to read bits from the input block. The main difference is that there are only two channels allowed and there’s single block per channel too. More curious thing is there are two revisions of this codec, with revision A having simpler bit allocation while revision B has additional tables (dependent on sample rate of course) to adjust how many bits per band will be eventually read. Also unlike successor there are no tricks to allocate fractional amount of bits per band, it’s always an integer amount of bits. From coding side it seems to be more or less straightforward MDCT with the only interesting trick is splitting frame data into sums and differences (not channels but the subsequent samples in frequency domain) and coding them in…