Atrac

An FFGL effect for Resolume Arena and Avenue. ATRAC, the perceptual coder MiniDisc used, does not throw detail away by resolution. It throws it away by bits: the signal is cut into overlapping blocks, each 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 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 is a consequence of that budget and that transform, and none of it is drawn: fine texture goes first because it is at the bottom 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 confine it; the allocation is recomputed every frame, so texture shimmers at low rates; and a cell that runs out of bits falls to grey.

On top sits the disc. A MiniDisc reads faster than it plays into a shock-proof buffer, and a knock stops the read. Here an audio onset, or the Knock button, is the knock: the buffer drains, and only if it empties does playback break and the picture hold until the buffer has refilled. Buffer, Read Speed and Knock Length are seconds and a multiplier, 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 with the cells the transient detector switched to short blocks tinted. 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.