Files We Actually Recognize (Shocking, We Know)

OnSong can transpose chords found in text-based chord charts. Using a feature called ChordFlow™, we can also peer inside of PDF files and transpose & format chords in place. (Yeah, we're basically wizards. You're welcome.)

Flip That Key Around (Enable Transposition)

By default, PDF files are displayed "as-is". That's because a PDF file is like a digital print out — it's basically just a picture of music, not actual musical data y'know? It doesn't usually contain the rich musical information found in text-based charts in the OnSong or ChordPro file formats. In this case, the Chords tab will display an "Uh… we need your help" overlay.

Tap on the Flip That Key Around button & OnSong does its bleepin' magic — recognizes the chords on the page & detects the key. The key is then saved to the attachment. This is what's required to transpose the song. If OnSong can't find a key in the PDF (which happens, srsly), Uhhh… We Got Nuthin' appears with the option to Figure It Out Yourself or Just Show Me Text. You can also manually twist the key in the Attachment Tweaks Screen if our robot overlords got it wrong.

ChordFlow™ reads the text in text-based PDF files to find the chords through some fancy pattern-matching shizzle. Scanned or image-only PDFs use on-device machine learning optical character recognition that recognizes chords & overlays new text-based chords in the same spot. Accuracy totes depends on how the PDF was put together though. Like, some charts might abbreviate "B" for bridge or "C" for chorus, which our algorithm will totally think are chords. Whoops.

Transpose Those PDFs Like a Boss

OnSong finds a key for the chart & chords are detected, you can transpose into a different key in the Style Preferences Chords tab. On iOS/iPadOS, the chords are whited out with the current paper color & PDF annotations get added. You can tap on these chords to open the chord inspector, or to hear what the chord sounds like. On Android, the PDF viewer itself handles the transposition instead of using PDF annotations. (Different strokes, y'all.)

Make Your Chords Pretty

Once transposition is enabled for a PDF, the Font Flavor & Highlight Explosion options show up. This lets you apply some formatting to the chords — like color & highlight — because apparently you care about aesthetics. ChordFlow™ attempts to match the font used in the original PDF file. It's like interior decorating, but for nerds.

Download Your Transposed Masterpiece

If you've downloaded a file from a content provider like PraiseCharts, you'll have access to transpose charts if you're signed into the service. OnSong will bug the content provider to download extra attachments in the key as needed. If you already have attachments with keys matching the attachment type, you can also transpose between them without an Internet connection. (Finally, something works offline!)