Plug a USB DAC into your phone and hear the file exactly as it is. Tune your headphones to your ears from measurements, and run the music on your PC from the same device.

CastFi takes the USB DAC directly instead of going through Android's audio path. DSD goes out unconverted, PCM in its original format. What is playing and in what format is on screen — nothing to guess.

■ What makes it different
• Headphones matched by measurement, not by feel. Instead of pushing sliders, pick the model you own.
• Ordinary tracks upsampled to DSD on the way out. If the phone struggles, the PC converts instead.
• The CastFi on your PC, driven from your phone. Anywhere at home, the PC's music is in your hand.
• No reason an audio app should be plain. A screen that follows the album's colors, high-resolution art.

■ Hear it as it is
Bit-perfect and exclusive output, native DSD (DoP included). When nothing plays, the device is released.
You don't need DSD files. Upsampling converts ordinary tracks like FLAC to DSD on the way out, at a rate set automatically from what your DAC and phone can spare. Short on headroom, CastFi tells you instead of quietly lowering the quality.

■ Sound that fits your ears
Headphone matching starts from measurements, not from pushing sliders by feel. Pick the model you use and its measured curve is corrected toward a target — another headphone's sound, or the Harman target as it is. Describe the sound you want in a sentence and CastFi builds it; refine the result with a precision EQ and save it.
Once the sound is straight, put your taste on top. Adjust with plain names — bass · vocals · clarity · air — and switch on the BASS+ · CLEAR+ · WIDE+ sound fields, speaker space and crossfeed. Changing a setting doesn't jump the perceived loudness. Leave them off and nothing is touched.

■ PC, NAS and the players at home
With the CastFi Windows app on the same Wi-Fi, the two find each other on their own. Control what the PC is playing from your phone, and change search, playlists, even the PC's headphone correction and presets from your hand. Bring PC tracks over to the phone and listen offline. Remote listening to the PC's music from outside the house is offered as a preview.
Music gathered on a NAS plays straight from the phone. Large files are read ahead so playback doesn't break up, and tracks can go to a network player (DLNA / UPnP) at home. It all connects directly inside the house, with no relay server outside.
Nothing is locked away just because you have no PC.

■ Cloud storage (OneDrive)
Pick a folder in your OneDrive and its music joins your library. Stream it, seek anywhere, and save the tracks you want to this phone for offline listening. CastFi only reads the folders you pick and never changes or deletes anything; your sign-in details and music files are not sent to our servers. Google Drive support is coming soon.

■ My music, only the folders I chose
CastFi doesn't quietly crawl the whole device. You pick the folders holding your music, and CastFi reads only those. Call recordings and messenger voice clips never get mixed into your library. Sorted by album · artist · track · folder, lists and queue hold up at tens of thousands of tracks.

■ Good to know up front
• It does not play music from streaming services on this phone, and there is no online search or purchase. It's an app for the files you own — on this phone, your PC, your NAS or your OneDrive.
• Direct USB DAC output needs a device supporting a USB Audio Class 2.0 DAC and OTG; the formats accepted differ from DAC to DAC.
• The PC link, NAS and network players need the same Wi-Fi, and the PC runs Windows 10 / 11.

Every feature works without a CastFi account (OneDrive uses your Microsoft sign-in). Anonymous usage stats and error reports can be turned off in Settings, and your music files are never uploaded to our servers. Available in 12 languages.

Windows app and full guide: https://castfi.castplan.net
Contact: support@castplan.net