VOX MACHINA

A USB Audio Engine for Android

A precision audio Engine for Android. Bypasses the audio stack entirely — AudioTrack, the mixer, HAL resampling, all of it. Output is raw isochronous USB to a DAC of your choosing. UAC1 and UAC2. No root required. The signal path is sacred, and the diagnostics prove it.

ENGINE

Three sovereign pipelines — Float32, Integer Passthrough, DSD Native. They don't share code. Bytes on disk become bytes on the wire, verified end-to-end.

Bit Perfect

DSD Native or integer PCM reach the DAC without float conversion, resampling, headroom, or DSP of any kind. The Engine admits only what the DAC can accept natively. Everything else is rejected with cause, not silently degraded.

Source Matching

The DAC runs at the source rate where possible. Resampling engages only when hardware demands it, and only the Iron Furnace resampler does it. The Engine seeks fidelity before convenience.

Wide

Maximum compatibility. The Engine finds the best available transport for every track, resampling when necessary, float pipeline when needed. Nothing fails to play.

Bit Perfect Lossless Processing Lossless Processing · ATT DSP Active DSP Active · ATT

Five fidelity tiers declare what the Engine does to your signal — with honest ATT suffixes when digital volume is engaged. The Engine does not lie.

THE SEALED WITNESS

Chain of Custody

In Bit Perfect sessions, the Sealed Witness takes the stand. It is a chain of custody from decoder to DAC — every byte your source produces is sealed and CRC hashed at origin, and every byte submitted to USB is verified against that seal.

The Witness holds the memory of what the signal was. It compares that memory against what the signal became.

The Engine does not merely claim bit-perfect. It proves it — live, on the pipeline card, while the music plays.

Diagnostics — URB integrity verified, Bit Perfect

DSD

Native DSD up to DSD2048 via TYPE_I_RAW_DATA for DACs that bear the mark and phones with the cycles to spare. Three transport rites, chosen by the Engine based on what the signal path requires.

DSD Native Raw 1-bit via TYPE_I_RAW_DATA. Bit-perfect. Sovereign. No framing, no compromise.
DoP DSD-over-PCM framing with standard markers. Broad DAC compatibility without native mode.
PCM Decimation DSD to PCM when the float domain is required. Confessed, not concealed. The Engine does not silently degrade.

Nothing is added. Nothing is taken. Every transformation is declared.

DIGITAL SIGNAL PROCESSING

Resampler

8,192-tap polyphase windowed-sinc FIR, built from first principles and accelerated by NEON-SIMD architecture. Engages only when source rate does not match the DAC's preferred rate. Four modes, settled at session assembly:

Mathematical Blackman-Harris, linear phase, ~92 dB stopband. Default.
Minimum Phase Zero pre-ringing via cepstral transform. Sharper transient attack.
Apodizing Minimum phase with relaxed bandwidth. Gentler HF rolloff. Meridian-inspired.
Brickwall Kaiser β = 14, >120 dB stopband. Steepest rolloff; longest ringing tail.

If source rate matches DAC, the resampler is not instantiated — absence, not bypass.

Equalizer & Convolver

31-band graphic or parametric EQ. Biquad filter Engine with per-band bypass, logarithmic Q, and direct gain entry. Automatic headroom attenuation scaled to your curve's peak boost.

~6,000 bundled open source AutoEQ profiles, searchable in-app for headphone correction. Import your own. Presets with save, load, and delete.

Convolution Engine loads WAV impulse responses end-to-end — AutoEQ, Oratory1990, REW exports — audible within ~500 ms of tapping Apply.

Under Bit Perfect, the processors are not instantiated. The float domain is not entered. Absence, not bypass.

Bit-Perfect Playlist

The Engine probes every track in your library against the connected DAC — format, sample rate, bit depth, channel count. Only tracks that reach the wire without processing are admitted.

Swap DACs, get a different list. Not a tag. Not a guess. A live hardware verification.

Bit-Perfect Playlist — live DAC scan in progress

TRANSITIONS

Gapless The chain between compatible tracks continues unbroken. The current track plays to its final sample; the next begins on the following sample. No tricks, no silence, no crossfade, no transport cycle.
Skip User-initiated next/prev within the same format execute as a pacing-thread-owned cut. No silence beyond the reservoir-refill window. No clicks, no pops, no rebuild on every tap.
Silent Transit On stop, the Engine submits silence before teardown. The DAC loses clock lock on your terms, not abruptly.

FURTHER

Digital Volume

Native post-reservoir gain on demand. Works under Bit Perfect with honest ATT labeling. Summons the float domain only when combined with EQ, convolver, or other DSP that genuinely requires it.

ReplayGain

Track and album modes. R128 and ReplayGain 2.0 tags, with a −5 dB R128 offset. Peak-required boost doctrine — the Engine refuses to amplify without a valid peak tag. Live enable/disable. Gapless albums gain-match continuously across track boundaries.

Channel Balance & Crossfeed

Per-ear compensation for asymmetric hearing. Crossfeed for binaural imaging on headphones. Auditory Compensation curve for open-back reference.

Library

Full scanner that goes beyond MediaStore — in-house parsers for DSF, DFF, WavPack, Opus edge cases, and filesystem roots Android's indexer refuses to touch. Artist, album, folder views. Sort, search, section index, fast scroll.

Queue & Playlists

M3U playlists. Persistent queue with a swipe-accessible queue rail. Add tracks mid-session without losing your place. Shuffle, repeat, insert-after-current.

Scrobbling

Last.fm and ListenBrainz scrobbling for the record keepers. The Engine listens honestly; it reports the same way.

Diagnostics

Every decision is visible. Simply tap and hold on the track's title or album art — the Engine reveals all.

The pipeline card shows the live chain: source format → pipeline domain → DSP stages → packer → transport. Integrity digest, transport strategy, drift counters, reservoir depth, starvation events.

Every transformation declared. Every fidelity tier earned. Nothing hidden, nothing assumed.