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A November 3 report describes using the Ultra Low Complexity Codec (ULC) to play 44.1 kHz stereo audio on Nintendo 64 at bitrates near Opus, with decoding said to use about 4% of the console’s CPU time. The result is a developer’s report, not an independently documented performance test; details such as exact bitrate and test conditions are not specified.
A developer has adapted the Ultra Low Complexity Codec (ULC) to play 44.1 kHz stereo audio on the Nintendo 64, reporting that decoding uses about 4% of the console’s CPU time. The November 3 report says ULC can approach Opus bitrates, a potential way to fit recorded music into N64 games without consuming most of a cartridge or slowing gameplay with expensive decoding.
The report comes from the developer of Xibalba 64, who says the game’s music currently occupies about 31 MB of its 32 MB ROM when stored using ADPCM, a compression method supported by the open-source Libdragon development environment. The game contains around 15 minutes of music. The developer calls that use of cartridge space wasteful and describes ULC as a more compact alternative suited to the console.
Libdragon already includes a real-time, RSP-accelerated Opus decoder, but the developer says it is too slow for continuous use during gameplay. The report also says an earlier MP3 approach on N64 could strain performance: Conker’s Bad Fur Day used RSP access to decode MP3 for speech, but the developer characterizes it as too demanding for music or effects running continuously during play.
ULC was created by Aikku93 for a Game Boy Advance audio demo and has been developed since 2019, according to the report. It is a transform codec that uses the Modified Discrete Cosine Transform, like MP3, but represents coefficients with a simple nibble-based scheme rather than Huffman entropy coding. That design avoids arbitrary bit reads and complex entropy decoding, which the report presents as key to keeping the decoder lightweight.
More Music Within N64 Limits
The reported result addresses a longstanding constraint of cartridge-based N64 games: recorded audio takes substantial storage, while decoding more advanced formats can compete with gameplay for limited processing time. If the stated performance holds in practical games, developers could use longer or higher-quality music without dedicating a large share of a ROM to audio or relying entirely on short samples arranged in the style of tracker music.
The claimed 4% CPU use is especially relevant because it suggests the format may leave more processing capacity available than MP3 or Opus decoding, as described by the developer. That could make continuous background music more feasible. The report does not establish that ULC will become a standard for N64 releases, but it offers homebrew developers another option for balancing sound quality, storage and performance.
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Why N64 Audio Was Constrained
The N64’s 93 MHz CPU and cartridge storage shaped its audio choices. Nintendo’s Libultra library provided RSP-assisted ADPCM playback, but a five-minute stereo track at 44.1 kHz would take about 12 MB in that format, according to the report. That was larger than the entire 8 MB Super Mario 64 ROM; the biggest N64 cartridges reached 64 MB.
Developers commonly used short samples triggered and mixed during play instead of storing complete music recordings. Nintendo restricted direct third-party access to the Reality Signal Processor (RSP) for much of the system’s life, though some later games gained access. The open-source Libdragon project provides tools for N64 development, including RSP-based audio decoding, and has made newer formats available to homebrew creators.
ULC’s origins also point to its design goal: Aikku93’s GBA demo reportedly played recorded music at about 70 kbps on hardware with a 16 MHz ARM CPU and no vector instructions. The N64 report says ULC can produce usable audio at 16 kbps, with quality reduced at that rate. These figures describe different operating points, not a direct comparison of identical audio tests.
““44100 Hz stereo with near-Opus bitrates using about 4% of the N64’s CPU time.””
— The developer reporting the N64 implementation
Performance Claims Need More Detail
The report does not give the exact bitrate used for the N64 demonstration, the audio samples or quality measures used in testing, or a breakdown of CPU use across different game conditions. It also does not provide independent benchmarks confirming the reported 4% CPU figure or near-Opus bitrate comparison. Those claims should be treated as the developer’s account rather than a verified result.
It is also unclear whether the implementation is ready for broader use, how it behaves with simultaneous game audio and music, or how much ROM space a complete game soundtrack would save compared with ADPCM. The report says ULC code is permissively licensed, but does not detail packaging, tool support or adoption by other developers.
Testing in More N64 Games
The next useful step would be publication of the N64 decoder and reproducible tests covering bitrate, sound quality and CPU load during gameplay. Wider testing could show whether the claimed performance applies across different tracks and game workloads, not only the developer’s project.
The report does not announce a release date, a finalized integration for Xibalba 64 or adoption by other N64 projects. For now, the development is a promising technical report; its broader impact will depend on implementation availability and independent results from developers using ULC on real hardware or well-documented emulators.
Key Questions
What is the Ultra Low Complexity Codec?
ULC is a transform audio codec created by Aikku93. It uses an MDCT and a compact nibble-based method for representing coefficients, designed to keep decoding relatively simple.
What N64 audio performance is being claimed?
The developer reports 44.1 kHz stereo playback at bitrates near Opus, using about 4% of the N64 CPU’s time. The report does not give the exact bitrate or testing methodology.
Why is ULC being considered for the N64?
N64 cartridges have limited storage, and the developer says decoding formats such as Opus can be too slow for continuous gameplay audio. ULC is presented as a way to reduce storage needs while keeping CPU use low.
Is the performance independently verified?
No independent verification is included in the source report. The figures are attributed to the developer, and more detail about test conditions and sound-quality comparisons is still needed.
Source: phoboslab.org
