Your music, untouched.

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No — Desibel plays your local and network files just fine on the device's own output. But it's built around sending audio to an external USB DAC bit-perfect, and that's the way it's meant to be used.

No — Desibel plays stereo (2-channel) and mono only. It's built for a two-channel USB DAC, so multichannel files (5.1 surround, quad, multichannel SACD rips) aren't played: tapping one shows a short "mono and stereo only" message instead of half-playing it. Multichannel isn't planned.

No — and that's on purpose. A DAC works in integer PCM, so a floating-point file can't be sent bit-perfect: it would first have to be converted to integer (re-quantized, and anything above 0 dBFS clipped). Rather than do that silently behind a "PCM LOCKED" badge, Desibel refuses a float file with a short message. Export or convert it to integer WAV/AIFF (16, 24, or 32-bit) — or FLAC/ALAC, which are always integer — and it plays untouched. Float is a DAW / mastering working format; the music files you play are almost always already integer.

Yes. DXD isn't a separate format — it's a name for high-rate PCM, 352.8 kHz at 24-bit (sometimes 32-bit), used as an editing format for DSD/SACD production (at 24-bit it carries exactly three times the data rate of DSD64, in the same 44.1 kHz clock family). On disk a DXD file is an ordinary WAV, FLAC or AIFF, so Desibel plays it bit-perfect through the normal PCM path — no special handling, no conversion — as long as your DAC locks the rate. One caveat: Desibel plays integer PCM only, and some DXD files are 32-bit float — if yours is, see the float question above.

Not by default — and never silently. Out of the box Desibel alters nothing: no resampling, volume, EQ or mixing; PCM (WAV/FLAC/ALAC/AIFF) and DSD-over-DoP play untouched. The only changes it can make are the opt-in output-matching conversions — DSD→PCM, PCM or DSD upsampling, and PCM→DSD — and each is off unless you turn it on in Settings and always badged gold ⟳ when it runs. See the two questions below.

There's a second case, but it's iOS, not the app: if the hardware can't lock a file's native sample rate, iOS resamples to a rate it can. Desibel never adds that conversion itself — it discloses it with the ⚠ RESAMPLED BY iOS badge so you always know.

And if you send audio somewhere other than a USB DAC — Bluetooth, AirPlay or the built-in speaker — that route can't carry bit-perfect audio at all; the ⚠ NON-USB OUTPUT badge tells you, so it's never mistaken for untouched.

They're optional output-matching conversions, all off by default — a fresh install is bit-perfect and never converts a sample. Some DACs sound their best fed a particular rate or format, so you can opt in to upsample PCM to a higher rate in the same family (up to 352.8 / 384 kHz), modulate 44.1-family PCM to DSD (DSD64–DSD256), or upsample DSD to a higher DSD rate (DSD128 / DSD256). You set them under Settings → PCM and Settings → DSD. The DSD modulation modes are CPU-heavy at the top rates — on a slower device, see whether your device can keep up below.

This is output matching for your DAC, not a fidelity improvement — manufacturing a higher rate can't add detail that wasn't in the file, and every conversion uses an exact integer ratio (no fractional resampling). Whenever one is on, the track is badged gold ⟳ (PCM UPSAMPLED, PCM→DSD LOCKED or DSD UPSAMPLED) — never a bit-perfect ✓ — so you always know. One honest note on PCM→DSD: 1-bit modulation needs a little headroom, so it plays about 6 dB quieter — a property of the conversion, not a hidden volume stage.

By whole-number (integer-ratio) interpolation — never a fractional resample. Each tier stays inside the file's own rate family, so the ratio is always a power of two: 44.1 kHz → 352.8 kHz is ×8, 96 kHz → 384 kHz is ×4, and so on. Desibel inserts the new sample slots and runs a polyphase FIR (finite-impulse-response) interpolation filter — a windowed-sinc low-pass by default, or the minimum-phase or apodizing variant you choose under Conversion filter — to reconstruct the band-limited waveform on the denser grid. Output is 24-bit integer; no dither or noise-shaping is applied or needed, because the re-quantization error sits about 144 dB down, far below any real recording's noise floor. Since the ratio is exact and same-family, no new frequencies and no pitch or timing error are introduced — it's the same signal, just carried at a higher rate. A file already at or above the tier's target is passed straight through (green ✓), never downsampled.

DSD is a 1-bit stream at a very high rate (DSD64 is 2.8224 MHz) whose quantization noise is sigma-delta-shaped up out of the audio band. Converting it to PCM — demodulating it — is decimation: a steep low-pass FIR (finite-impulse-response) filter removes that ultrasonic shaped noise, and the stream is downsampled by an exact factor of 32, so DSD64 → 88.2 kHz, DSD128 → 176.4 kHz and DSD256 → 352.8 kHz, at 24-bit integer. The low-pass is the same selectable filter used everywhere else (linear-phase, minimum-phase or apodizing). The ÷32 factor is fixed, but you can cap the result lower with Max PCM rate if your DAC won't lock the natural target. This runs only when you set DSD Output to Decode to PCM; by default DSD plays natively over DoP with no demodulation at all.

In two stages, and only for 44.1-family PCM so the ratio to the DSD rate is a whole number (44.1 kHz to DSD64 is ×64, to DSD256 is ×256). First the PCM is interpolated up to the DSD sample rate in one fused integer-ratio step. Then a high-order (5th-order) sigma-delta modulator — an error-feedback loop that shapes quantization noise up out of the audio band, the same principle a DSD recorder uses — re-quantizes it to the 1-bit DSD stream, which is packed into DoP for the DAC. The loop runs per channel with independent state; its noise-shaping response is tuned for stability (peak gain held near 1.5×), and because a 1-bit loop can sing idle tones on pure tones, DC or digital silence, the comparator is dithered with a small triangular-PDF (TPDF) noise to break them up. One honest consequence: a 1-bit modulator needs headroom, so the input is attenuated by a fixed 6 dB — a deliberate, disclosed property of the conversion, not a hidden volume stage. Because DSD is a 44.1-based rate, 48-family PCM (48 / 96 / 192 / 384 kHz) has no integer path to it and is never modulated — it upsamples or plays native instead.

There's no direct way to re-rate a 1-bit stream, so Desibel composes the two conversions above: it demodulates the DSD file down to high-rate PCM (the decimating low-pass), then re-modulates that PCM up to the chosen rate with the same 5th-order sigma-delta modulator, and sends the result over DoP. Most SACD and DST rips are DSD64, so this is what feeds a DSD128- or DSD256-preferring DAC a higher-rate stream. It's two conversions in series — which is exactly why it's badged gold ⟳ DSD UPSAMPLED, never a bit-perfect ✓, and why a file already at or above the target is left as native DSD instead.

Desibel runs on a wide range of hardware (any iPhone or iPad that can run iOS 17 or newer), and everyday playback is light: bit-perfect PCM and DSD, and PCM upsampling, run comfortably on any supported device. The two CPU-heavy modes are PCM→DSD modulation and DSD upsampling at the higher rates — DSD128 and especially DSD256 — because the 1-bit sigma-delta modulator has to run in real time on every single sample.

On a slower or lower-powered device, those top rates may not keep up. If that happens you may hear a brief dropout, and if it still can't sustain the rate Desibel stops and tells you rather than playing glitchy or noisy audio — it never drops the DoP lock into noise, so you're never left guessing. The fix is simple: pick a lower DSD rate (DSD64 is comfortable on far more devices) or use a lighter mode. Newer, faster devices have ample headroom for DSD256. Since these modes are opt-in and off by default, none of this affects ordinary bit-perfect playback.

DST is the lossless compression used by many DSD and SACD rips (it roughly halves the file size). Desibel decodes it transparently: a DST-compressed .dff or SACD track plays like any other DSD — native over DoP (bit-perfect) by default, or through the DSD→PCM conversion if you've set DSD to Decode to PCM for your DAC — with nothing extra to switch on for DST itself. Because DST is lossless, native DoP of a decoded DST track is genuinely bit-perfect. The player labels a DST track DSD64 (DST) in its format line, so you can always see when the DSD came from a DST-compressed source. If a DST file ever gives you trouble, please get in touch.

Yes — Desibel plays tracks straight out of a SACD disc image (.iso), with no extraction needed. Open the .iso in the browser like a folder and its tracks are listed; tap one and it plays the stereo layer bit-perfect as native DSD (DSD64) over DoP, exactly like a .dsf or .dff file — same badge, same gapless playback between tracks. Only SACD images work: a regular audio-CD or data .iso shows no tracks. Multichannel layers aren't played (stereo and mono only), and DST-compressed discs — most SACD rips — are decoded losslessly.

Three modes under Settings → DSD → Output, with Play as DoP the default:

Play as DoP (default) — plays DSD bit-perfect as native 1-bit DSD over DoP. Strict: if your DAC won't lock the carrier rate it stops and tells you rather than convert (resampling a DoP carrier would be noise, not graceful degradation). Decode to PCM — converts DSD to PCM, for a DAC that can't do DoP at all; badged ⟳ DSD→PCM LOCKED. Upsample — re-modulates a lower-rate DSD file up to DSD128 or DSD256 over DoP, for a DAC that prefers a higher rate; badged ⟳ DSD UPSAMPLED.

There's no automatic mode: a DAC's DoP support can't be probed reliably, so the honest default is strict native DoP, and you switch to Decode to PCM yourself if your DAC needs it.

The Conversion filter (its own section in Settings) sets the interpolation/decimation filter used by any conversion — decoding DSD to PCM, upsampling PCM, or upsampling DSD: linear-phase (default) (sharp, symmetric ringing), minimum-phase (no pre-ringing), or apodizing (gentle roll-off, minimal ringing). Linear-phase is the default because it's the most neutral — flat magnitude, no phase shift — and at these high rates its pre-ringing sits in the inaudible ultrasonic range. The others are there if you prefer their trade-offs. It takes effect on the next track, and only bites when something is actually being converted — native DSD over DoP and untouched PCM never touch it.

It only matters when you set the DSD Output mode to Decode to PCM. Desibel decodes DSD to PCM at the file's native rate ÷ 32 — DSD64→88.2, DSD128→176.4, DSD256→352.8 kHz. If your DAC can't lock that rate, iOS resamples the result (the ⚠ RESAMPLED BY iOS badge) — a second, uncontrolled conversion. Set Max PCM rate to the highest rate your DAC actually locks and the decode is capped there instead, so it lands on a rate the DAC holds and locks cleanly (⟳ DSD→PCM LOCKED) — a single, controlled conversion. Example: a DAC that tops out at 192 kHz locks 176.4 but not 352.8, so set 176.4 kHz and DSD256 decodes to 176.4 and locks, instead of decoding to 352.8 and being resampled.

The default is No limit (decode at DSD÷32), which is right for DACs that lock the high rates. If you don't know your DAC's ceiling, the rate probe (Settings → Probe output sample rates) shows exactly which rates lock. It's a one-time manual setting on purpose — deliberately simpler than having the app auto-detect and track every DAC.

No, by design — a software volume would alter the samples. Desibel outputs every file at its full digital level (0 dBFS) and leaves volume to your DAC or amplifier. Turn your amp down before you press play. Full-scale output can be extremely loud and may damage your hearing or your equipment — use it at your own risk.

From anything that appears in the iOS Files app — a NAS over SMB, WebDAV, Dropbox, iCloud Drive or files stored locally. You add sources as folders; Desibel browses them live, with no library to build. This is deliberate: Desibel contains no networking code and keeps no credentials — you set up the connection once in Files, and the app just reads through it.

By design the browser stays focused. By default it lists your playable music plus the cover art and booklets that live in the folder — images and PDFs — and hides everything else, so stray files don't clutter it. Two toggles under Settings → Browsing change what shows:

Show only supported files (on by default) — turn it off and the files Desibel can't play are listed too, greyed out and non-playable, so you can still see what's in a folder. Show artwork & documents (on by default) — turn it off to hide the images and PDFs as well. So a file you have but can't play — a lossy .m4a (AAC), say, or some other unsupported format — only appears with the first toggle off.

Network and cloud files are read ahead into a buffer so playback rides out brief stalls. Two settings under Settings → Streaming control it. Streaming buffer is how far ahead a track is buffered while it plays — the cushion against network hiccups. Start pre-buffer is how much is filled before a track starts playing: a lower value (the default is 0.4 seconds) starts almost instantly and stays responsive, while a higher one waits a little longer before the first sound but rides out a slow first read from a cold or distant source. Local files start instantly either way.

Not sure what to choose? Settings → Source speed has a Test source speed button that reads a file from each source and reports its throughput and first-byte latency, then suggests a streaming buffer and start pre-buffer to match — a fast local NAS suggests the smallest values, a slower or more distant source larger ones. It's only a suggestion; you set the final values yourself.

The truth about each track, read on two simple axes. The label names the locked state: PCM LOCKED or DSD LOCKED when the DAC is locked to the file's native rate; one of the gold conversion labels when an opt-in conversion is on — DSD→PCM LOCKED, PCM UPSAMPLED, PCM→DSD LOCKED or DSD UPSAMPLED; RESAMPLED BY iOS (⚠ — iOS had to resample; it still plays, you're just told); or NON-USB OUTPUT (⚠ — you're not on a USB DAC, so the output can't be bit-perfect at all: Bluetooth, AirPlay or the built-in speaker). The symbol is whether anything left the clean bit-perfect path: ✓ (green) means untouched, ⟳ (gold) means a disclosed conversion you turned on, and ⚠ (red) means the audio left that path — iOS resampled the rate, or you're on a route that can't be bit-perfect. A detail line under the badge traces the file to your DAC (for example DSD64 → PCM 88.2 kHz), so you're never left guessing.

Not from software alone — and no iOS app can. iOS doesn't expose what the DAC physically receives, so the in-app badge only confirms the sample rate locked. To prove the rest, Desibel includes built-in Test Signals: play a reference signal, record it off the DAC on a computer, then bring the recording back and check it on-device under Settings → Analyze a recording. See the next question for which signal to use.

Desibel generates reference signals on the fly (a built-in source in the picker). They're grouped the same way as in the app:

Demo — just checking the chain works. Tape click PCM and Tape click DSD are soft, warm ticks generated live at any rate (PCM from 44.1 kHz up, or DSD64–DSD256). Play one to hear that playback works and watch the status badge as the rate locks (or falls back). Not a bit-perfect check; nothing to capture.

Measurement — speaker/room calibration. Pink noise is a signal you play back and measure acoustically with a mic or SPL meter. It isn't a bit-perfect check and doesn't go through the analyzer.

Analysis — bit-exact. Record the DAC's digital input — an S/PDIF tap clock-locked to the incoming stream, or the USB link with a protocol analyzer (as in the screenshots above). Use PRNG sequence or Walking-bit for a true sample-for-sample byte compare — the proof that every bit arrived intact. (Recording the DAC's analog output can't prove bit-perfectness — the conversion's own gain and noise floor make an exact comparison impossible — so Desibel doesn't pretend to; it verifies the digital output, which is the part it's responsible for.)

For these signals, capture the output and check it under Settings → Analyze a recording. Each carries a self-describing header with a random per-run ID, so the app identifies it straight from the recording (nothing to note down) and a match can't be a coincidence. For the bit-exact pair (PRNG sequence and Walking-bit), set your recorder to lock its clock to the incoming stream — otherwise the two clocks drift and the sample-for-sample compare won't line up. These verify the native PCM path, so they won't play while PCM upsampling or PCM→DSD conversion is switched on — turn those off in Settings to run them.

They're generated on the fly. Nothing is bundled or stored: every signal is computed by code the moment you play it — sample by sample, at whatever rate you pick — so they add almost nothing to the app's size and each one exists at every supported rate. The Tape click DSD goes a step further and is modulated into a true 1-bit DSD stream live as it plays.

No. It's a folder player by design. Play a single track or a whole folder as a queue. Nothing to index, nothing to sync.