Supported Files

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 and format chords in place.

Enable Transposition

By default, PDF files are displayed "as-is". That's because a PDF file is like a digital print out. It doesn't usually contain rich musical information found in text-based charts in the OnSong or ChordPro file formats. In this case, the Chords tab will display an Enable Transposition overlay.

Tap on the Enable Transposition button and OnSong recognizes the chords on the page and detects the key. The key is then saved to the attachment. This is what is required to transpose the song. If OnSong can’t find a key in the PDF, No Key Detected appears with the option to Extract and Edit or Use Text Version. You can also adjust the key in the Attachments Properties Screen if it was detected incorrectly.

ChordFlow™ reads the text in text-based PDF files to find the chords through pattern matching. Scanned or image-only PDFs use on-device machine learning optical character recognition that recognizes chords in the song and overlays new text-based chords in the same location. Accuracy of chord detection does depend on the how the PDF file was authored. For instance, some charts may feature text-abbreviations for bridge or chorus which may interpret "B" and "C" as chords.

Transposing PDF Files

OnSong a key is available for the chart and 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 and PDF annotations are added. You can tap on these chords to open the chord inspector, or to playback the chord. On Android, the PDF viewer itself handles the transposition instead of using PDF annotations.

Formatting Chords

Once transposition is enabled for a PDF, the Font Style and Highlight Color rows appear. This lets you apply some formatting to the chords such as color and highlight. ChordFlow™ attempts to match the font used in the original PDF file.

Downloading Transposed Files

If you've downloaded a file from a content provider like PraiseCharts, you will have access to transpose charts if you are signed into the service. OnSong will contact the content provider to download additional 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.