Archive for the ‘Lossless Audio’ Category
A look on Perfect Clarity Audio
Friday, March 28th, 2025
Since Paul asked me to look at it (and what’s equally important, provided the binary to look at), I did exactly that.
It turned out to be a rather simple codec, originally known as Sonic Foundry Lossless. The only really interesting detail is that it has intra- and inter-frames. Intraframes start with 0xFFFFFFFF and four last samples for each channel (for filtering purposes). Each frame stores the number of samples (I suppose), coded data size, Rice code parameter (per channel), filter method/order (ditto), LPC coefficients (same, only if global flags enable it though) and probably CRC.
Data is coded as fixed-parameter Rice codes (low bit is used for the sign)—unless it’s filter method 5 which means all zeroes, then optional LPC phase (LPC has order four and 8-bit coefficients) and then, depending on filter order, fixed prediction as in Shorten.
Finally there may be mid/stereo reconstruction (if global config signals it) and clipping for 24-bit mode (but not for 16-bit apparently).
I don’t know if they’ve added some improvements in the newer versions but this looks rather simple compared to other lossless codecs. There’s the final bit of weirdness: it’s usually stored in WAV which means it’s one of those codecs with variable-size frames in WAV. Not something I’d like to support.
P.S. I’ll document it for The Wiki (as well as DVC from the previous post) a bit later.
Posted in Lossless Audio | 2 Comments »
Looking at the (un)Original Sound Quality format
Tuesday, June 27th, 2023
I was asked to look at it and since I have nothing better to do, I finally did.
OSQ was a format used by WaveLab mastering software for storing lossless compressed audio (they seem to have dropped support for it in the more recent versions). Internally it’s a clone of ages-old Shorten which does not even have LPC mode, only fixed predictors.