Middle C & Octave Offset

Default Value for Middle C

The general MIDI 1.0 specification does not explicitly define a pitch for middle C but it does consider middle C to be note number 60. The MIDI Tuning Standard states that note number 69 should be tuned at 440Hz by default, which would make middle C (60) to be C4. However, different manufacturers have assigned middle C to various octaves/pitches (usually C3, C4 or C5).

In accordance with the MIDI Tuning Standard and the scientific pitch notation, WEBMIDI.js considers middle C (261.626 Hz) to be C4 by default.

Offsetting Middle C

You can offset the reported note name and octave by using the octaveOffset property of various objects. This will make it easier to interface with devices that do not place middle C at C4.

Inbound Note Example

If your external MIDI keyboard sends C3 and WEBMIDI.js reports it as C4, it is because your keyboard places middle C one octave lower than WEBMIDI.js does. To account for that, simply set WebMidi.octaveOffset to -1. This way, when your keyboard sends C3, WEBMIDI.js will also report it as C3.

In both cases the actual note number (60) remains the same. It is just being reported differently.

Outbound Note Example

If you are sending F#4 to an external device and that device thinks it's receiving F#5, it means that the external device places middle C one octave higher. In this case, set WebMidi.octaveOffset to 1 to account for the difference.

Offsetting Granularity

For most scenarios, setting the global WebMidi.octaveOffset is enough. However, the octaveOffset property is available for several objects to allow for better granularity:

• Input
• InputChannel
• Output
• OutputChannel
• Note
• WebMidi

If you define octaveOffset on several objects, their value will be added. For example, if you set WebMidi.octaveOffset to -1 and set octaveOffset on a specific channel to 1, the resulting offset on that channel will be 0 (-1 + 1) while the offset on other channels will be 1.