Atrac

An FFGL effect for Resolume Arena and Avenue. ATRAC, the perceptual coder MiniDisc used, throws detail away by bits rather than by resolution. The signal's cut into overlapping blocks, each one goes through a modified discrete cosine transform, the coefficients are grouped into block floating units with a scale factor and a word length each, and a fixed budget of bits per block is shared out by a masking model, so a band sitting next to a loud band gets few bits or none.

Atrac runs that coder on the picture as a separable two-dimensional lapped transform with a fixed budget per cell. Every artefact comes from that budget and that transform, and none of it is drawn on. Fine texture goes first because it's at the back of the queue. A hard edge rings one block either side because quantisation noise is a sum of basis functions over the whole window, and short blocks keep it in. The allocation is worked out again every frame, so texture shimmers at low rates. And a cell that runs out of bits falls to grey.

On top of that sits the disc. A MiniDisc reads faster than it plays, into a shock-proof buffer, and a knock stops the read. Here the knock is an audio onset or the Knock button. The buffer drains, and only if it runs dry does playback break and the picture hold until the buffer's refilled. Buffer, Read Speed and Knock Length are in seconds and a multiplier, worked out in double on the CPU.

Show Bits paints every cell as its own coefficient plane, with each band's word length as heat, and Show Blocks draws the grid and tints the cells the transient detector switched to short blocks. Modelled on ATRAC-style coding from the published description of the format; ATRAC and MiniDisc are trademarks of Sony Group Corporation, and this project is not affiliated with or endorsed by Sony.