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A November 3 report describes using the Ultra Low Complexity (ULC) audio codec to play 44.1 kHz stereo on Nintendo 64 hardware at bitrates near Opus, while using about 4% of the console’s CPU time. The result could substantially reduce the cartridge space needed for recorded music, but the performance and quality figures come from the developer’s account; independent verification and fuller test details are not provided.
A developer writing about the N64 game Xibalba 64 says the obscure Ultra Low Complexity (ULC) codec can play 44.1 kHz stereo audio on the console at bitrates near Opus while using about 4% of the N64’s CPU time. If the reported results hold in practice, ULC could make recorded music far less costly in cartridge space than the ADPCM audio the developer had been using.
In a post published November 3, the developer said roughly 31 MB of Xibalba 64’s 32 MB ROM had been devoted to music and sound stored as ADPCM. That approach worked, but the developer described it as wasteful: the game contains about 15 minutes of music, while the audio takes up nearly the entire ROM. The post says the ULC experiment produced full-rate stereo playback using a small share of the console’s CPU resources.
ULC was created by developer Aikku93 for a Game Boy Advance audio player and has been developed since 2019, according to the report. It is a transform codec: it converts slices of audio into frequency-domain coefficients using the Modified Discrete Cosine Transform. Rather than use MP3-style Huffman entropy coding, it packs values into a simple, nibble-based format that the author says is less demanding to decode.
The report describes ULC as capable of usable results at 16 kbps, while acknowledging that quality falls at that rate. It does not provide a standardized listening test or a detailed benchmark methodology for the N64 figures. The claims about bitrate, audio quality and CPU use should therefore be read as the author’s reported results, not as independently verified measurements.
More Music, Less Cartridge Space
The N64’s limited storage made continuous recorded music difficult. The report estimates that five minutes of 44.1 kHz stereo audio encoded with the platform’s ADPCM approach would take about 12 MB, more than the total ROM used by Super Mario 64, which the author gives as 8 MB. Developers commonly used short samples triggered in sequence instead of storing whole music tracks.
A codec that decodes efficiently on the N64 could change that trade-off for homebrew and other projects. Lower storage needs could leave room for more music, dialogue or game content without requiring a larger ROM. The reported 4% CPU use also suggests less processing overhead than the MP3 decoding used in some later N64 games, although the post does not establish how the decoder performs alongside different gameplay workloads.
The result is relevant beyond the N64 as an example of how a codec designed for modest hardware can find a use on another constrained platform. It does not, by itself, show that ULC is ready to replace established codecs broadly or that every game can use it at the same performance and sound quality.
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N64 Audio’s Storage Trade-Off
The N64 used cartridges, where storage space was limited compared with the PlayStation’s CD format. Nintendo’s Libultra library included an ADPCM decoder that used the console’s Reality Signal Processor, or RSP, to decompress audio during playback. According to the report, this reduced sample storage needs but still left full-length stereo recordings expensive in ROM space.
Third-party developers initially had limited access to the RSP, the post says. Some later projects could use it directly: the author cites Conker’s Bad Fur Day as a game that decoded MP3 speech audio, while reporting that the computational cost made MP3 unsuitable for continuous background music or sound effects during gameplay. The open-source Libdragon development environment offers RSP-accelerated ADPCM and Opus decoders, but the author says Opus was too slow for the intended in-game use.
The developer says ULC appeared promising after encountering an existing Game Boy Advance demo that played recorded music at 70 kbps. The codec’s straightforward coefficient format avoids arbitrary bit reads and more involved entropy decoding, according to the post. That design choice is presented as a reason it can run on low-powered processors; the N64 application is a new use of the codec, not a newly announced codec release.
Performance Tests Still Limited
The post does not specify the exact ULC bitrate used for the 44.1 kHz stereo N64 result, provide audio samples for a controlled comparison, or explain how the reported CPU share was measured. “Near-Opus bitrates” is not paired with a precise bitrate or test conditions in the supplied material, so the size and quality gains cannot be independently assessed from the report alone.
It is also unclear how the decoder performs across different games, sound mixes and hardware configurations, or whether the reported CPU use includes all playback-related work. The author says low-bitrate ULC can be usable but that sound quality suffers at 16 kbps. No independent testing, broader adoption, or final release plan for the N64 implementation is described.
Testing in More N64 Games
The immediate next step is practical testing: running the decoder in more demanding game situations and publishing the chosen bitrate, CPU measurement method and listening comparisons. Those details would help developers judge whether the claimed savings translate into reliable playback during gameplay.
The report does not announce a release date or a wider rollout. ULC’s code is described by the author as permissively licensed, which may allow other developers to examine and adapt it. Whether it becomes a common option for N64 projects will depend on reproducible performance, acceptable audio quality and the effort required to integrate it into existing tools.
Key Questions
What is ULC?
ULC stands for Ultra Low Complexity Codec. It is a transform-based audio codec developed by Aikku93, using the Modified Discrete Cosine Transform and a compact nibble-based format for audio coefficients.
What does the developer claim it can do on N64?
The developer reports 44.1 kHz stereo playback at bitrates near Opus, using about 4% of the N64’s CPU time. The supplied report does not give enough test detail to treat those figures as independently verified.
Why does this matter for N64 games?
Recorded music can consume substantial cartridge space. The author says ADPCM music used about 31 MB of a 32 MB ROM for Xibalba 64, so a more compact format could leave more room for game content.
Is ULC already a proven replacement for ADPCM or Opus?
No. The report describes one developer’s N64 implementation and its claimed performance. It does not provide independent benchmarks or establish that ULC will match established codecs across different games and audio conditions.
Source: phoboslab.org
