Incoming signal
Original file
Every single bit of your FLAC · WAV · ALAC, untouched.
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FIDEL starts from playing the sound in your files without changing a single bit. And when you want more, it can precisely restore lost highs and squashed dynamics. What to turn on is entirely up to you — this guide explains what each feature does and when it's worth switching on.
FIDEL's starting point is Bit-Perfect — sending the sound in your file exactly as it is to the DAC, with no resampling, correction, or EQ. Turn off every processing option and you're automatically in this state, and the gold BIT-PERFECT badge lights up on the Player screen.
Every single bit of your FLAC · WAV · ALAC, untouched.
Output as-is, with no mathematical conversion in between.
Every feature in FIDEL lives in one of these four places.
The main screen for what you're listening to now. Album art, audio quality info, playback controls, the live spectrum, and the Signal Path showing what processing the signal is passing through — all in one place.
Where you add and organize your music. Create folders, import files, tap a track to play it. Swipe left to move between folders, swipe right to delete.
Shape the tone to your taste. Pick a preset or adjust all 10 bands yourself, and import headphone correction profiles.
Home to every switch for audio processing and playback behavior. Most of the features described below live here.
Restore what's lost to lossy compression or heavy mastering. Each process is set with an intensity slider — just switch it on when you need it.
MP3 and AAC cut off everything above a certain frequency (usually around 16 kHz) to save space. HFR analyzes that missing high end and fills it back in. Higher intensity extends further into that range.
When to use — When low-bitrate MP3/AAC sounds dull. Not needed for files that are already hi-res.
Generates harmonics for the highs above 16 kHz lost to lossy compression, gently restoring the sound's "air" and openness.
When to use — Very lightly, when sound feels closed-in and dull.
Adds harmonics to the low end for bass that feels present without turning muddy. Fills in the bass small earphones can't reproduce.
When to use — When bass feels thin on earphones or small speakers.
For sources squashed loud by the "loudness war," this pulls quiet passages further down to widen the contrast between soft and loud.
When to use — When modern pop feels loud and flat from start to finish.
Raise and lower 10 bands from bass to treble to change the character of the sound. Start with a preset, then fine-tune every single band if you want.
Pick one of Flat · Rock · Jazz · Classical · Pop · Bass Boost · Vocal and you're done. Custom settings can be saved under a name (no limit on how many, long-press to overwrite or delete) and recalled anytime.
Switch on Parametric mode to adjust frequency, gain, and Q (width) per band, or import an AutoEQ headphone correction profile straight from the internet. Tailor the sound exactly to your headphone model.
Headphones split left and right so hard that sound tends to bunch up inside your head. FIDEL spreads it out naturally, more like listening to speakers.
Blends a touch of the left channel into the right ear (and vice versa), creating the natural soundstage of sitting in front of speakers. Especially good for old recordings with extreme left/right separation.
Simulates a pair of stereo speakers in front of you, spreading the sound outside your head. A more refined approach than crossfeed.
Adjusts how far left and right the sound spreads, from Mono (0) — Original (1.0) — Expanded (2.0). Double-tap the slider to reset to 1.0×.
Two ways to place your music inside a room, hall, or cathedral. Both are Pro, and both color the sound — so switching either on clears the BIT-PERFECT badge.
Studio · Live Club · Concert Hall · Cathedral presets with an amount control (default: Live Club, 35%). It rides on HRTF rendering to wrap the space around your head, so turning Reverb on also turns HRTF on (and off with it). A ~180 Hz high-pass keeps the low end tight instead of muddy.
When to use — A quick, natural sense of space with no files to hunt for.
Load a real impulse response (WAV/AIFF) measured in an actual hall or cathedral, and your music takes on that exact space — the most realistic "you are in the room" reverb. FFT-based so multi-second tails run in real time; a Mix control blends dry and wet, and the IR is level-normalized so it can't blast.
When to use — Maximum realism. IRs aren't bundled — load your own (e.g. OpenAIR, EchoThief).
Both "raise the rate," but for different reasons. Especially useful if you're running a hi-res external DAC.
Precisely interpolates 44.1/48 kHz sources up to a higher rate — 88.2 · 96 · 176.4 · 192 kHz — before sending them to the DAC. Sound quality improves when this software conversion outperforms the DAC's internal filter.
When to use — Alongside a hi-res external DAC.
Runs only nonlinear processing — EQ, saturation — at 2× or 4× the rate, pushing the noise (aliasing) that creates into a range you can't hear.
When to use — When pushing EQ or an exciter hard. Higher multipliers use more battery.
Precisely correct room or headphone characteristics using an impulse response (IR) file you provide. Load an AutoEQ headphone IR, a room IR measured with REW, or similar.
Match left/right volume (double-tap to center), flip absolute phase per channel, and boost the bass and treble that get lost at very low volumes.
Merges left and right so both ears hear the exact same sound. Useful for listening with one earbud, or safely playing files with a broken channel.
Stitches tracks together frame-by-frame with no silence in between. Essential for live albums, classical, and DJ mixes that shouldn't be interrupted.
The previous track fades out as the next fades in. A curve that avoids a volume dip midway keeps the transition smooth.
Randomize the queue (keeping the current track's position) or cycle through off · repeat all · repeat one. Buttons at either end of the screen.
Automatically evens out volume differences between tracks so the next song doesn't suddenly jump louder or quieter. Uses ReplayGain tags when present, or automatic analysis otherwise.
Once playback starts it keeps going in the background like any music app, with the current track's info and controls on the lock screen and Control Center. Playback automatically pauses for incoming calls and resumes afterward, and it pauses on its own when you unplug your headphones or lose the Bluetooth connection.
Album art, title, artist, and playback progress appear on the lock screen and Control Center, where you can play/pause and skip to the previous or next track.
Reopen the app and the last track you were listening to is right there, ready to go. (It doesn't auto-play — just tap the play button to start.)
Re-reads tags, album art, and format info from every file. Use this if artwork or info looks wrong even though the files haven't changed.
Choose the bit depth when converting files to FLAC. 24-bit is a transparent archive; 16-bit is roughly a third smaller. DSD can be converted to FLAC too.
Copy every file and folder to a destination like iCloud Drive as a backup. Deleting the app also deletes your library, so back up beforehand.
Choose AirPlay, Bluetooth, or the built-in speaker right within the app. Switches automatically when you plug in headphones or pair Bluetooth.
Shows the filename as the track title instead of the tag. Handy when you organize your library by renaming files.
Requests the DAC's native rate and a small buffer to avoid extra OS-level conversion, and lets you adjust the spectrum analyzer's bands, slope, and frame rate.
Here are the most common situations and a good first setting to try. If you're unsure, turn everything off and start with the original sound.
In the Library tab, tap + in the top right → Import Files. Pick multiple tracks at once from your iPhone, iCloud, or an external drive.
Tapping a track makes that list the playback queue and takes you to the Player screen. You can also create folders to organize by album or genre.
With nothing turned on, you're at BIT-PERFECT by default. Use this sound as your baseline.
In Settings, use the recommendation table above and switch on what you need, one at a time. Every setting can be reverted at any time.