Amiga Programmer Breaks Sin-Dots Record with Zero-CPU Atari Audio Emulation
A new technical optimisation in the demoscene allows for high-fidelity Atari YM2149 emulation without consuming main CPU cycles, surpassing Hannibal’s previous benchmark.
Amiga programmer Arnaud Carré has set a new benchmark in the demoscene by breaking the sin-dots record with 7,210 dots rendered at 50 frames per second. The achievement was made possible by a novel technique that emulates the Atari YM2149 audio chip on the Amiga with zero CPU overhead, effectively removing the Motorola 68000 from the playback loop. This performance surpasses the previous record of 6,682 dots established by demoscene figure Hannibal.
The project was initiated in response to a challenge from Hannibal, who had previously surpassed Carré’s earlier record of 6,405 dots. Hannibal’s message suggested that Carré, described as an Atari programmer, had not fully optimised the Amiga’s capabilities. Determined to respond, Carré sought a method to play Atari music during the dot-rendering process without the significant CPU cost associated with full hardware emulation, which previously consumed up to 50 per cent of frame time.
Carré’s solution utilised the Amiga’s PAULA audio chip and its 'attached voice' mode. This feature allows one voice to modulate the volume of another, a function rarely used in practice. By storing a triangle wave as an 8-bit sample and using a square wave as a 16-bit modulator, Carré reversed the standard data flow. This adjustment eliminated the low-resolution artifacts that plagued his initial attempts, producing the complex, sweeping timbres characteristic of the 'MadMax buzzer' effect pioneered by Jochen Hippel.
To achieve the promised zero CPU usage, the technique relied on the COPPER coprocessor. Carré pre-generated COPPER lists for each music frame, containing all necessary register updates for the PAULA chip. The COPPER executed these instructions in parallel with the main CPU, handling all audio state changes automatically. This allowed the 68000 to dedicate its entire processing power to rendering the sine-wave dots, with no instructions consumed by the audio driver.
The resulting demo featured Atari music composed by BigAlec, showcasing the MadMax buzzer effect. The technical feat demonstrates how specific hardware features of legacy systems can be leveraged to offload processing tasks, achieving a level of efficiency that standard emulation drivers cannot match. The new record stands as a testament to deep hardware understanding within the retro computing community.
