Another New Version

This new release comes in two alternative versions: pjpeg092.bin non-compressed, and pjpeg092.mbz compressed. Both are actually multiboot programs and run from EWRAM, although this is invisible to the user. The .mbz version takes up less cart space and has other space-saving virtues. This version is now power-saving! and the source code is available.

How the MIDI file is played

Unlike the version in Book Reader this player works with MIDI files as they are found, with no re-processing. This means more work at the time they are played as the midi clock has to be reconciled with the asynchronous frame rate.

The approach here was to check once per frame (about 1/60 sec) how many midi clocks had passed (keeping track of the fractional midi clocks) and checking the file for events for each midi clock. This has the effect of moving all events to the nearest tick of the frame rate clock. This does not appear to be noticable.

Events in the MIDI file cause 'Note On' and 'Note Off' commands. These cause changes to an 8 voice wide array of currently playing notes (or percussion sounds). If a note is to be started, the array is searched for an unused voice. If none is found then the oldest playing note is stopped to make room.

The mixer uses this array to determine which samples to mix for the current frame. Two 304 byte buffers are used for the mixer to write to on a given frame, and another two are simultaneously being transferred to the sound FIFOs using DMA at 18157Hz. Each buffer has 4 voices mixed into it. The output of the 2 FIFOs is mixed into both left and right channel to produce a mono sound output.

This approach allows more accurate sound samples than if 8 voices were mixed into the one buffer. The original samples have to be restricted in amplitude so that adding several channels together does not cause the sum to exceed the available range. The more channels mixed together, the lower the permissible amplitude of each channel and the more distortion (digital noise) which will be produced.

The mixer is written in C, so is not particularly fast. It is completely sufficient for the current application. I may optimise it in assembler for something to do in the future.

Other MIDI commands which are currently processed are Set Channel Volume, and Set Tempo.

Limitations

• The available sound samples currently include Organ, Harpsichord, Strings, Trumpet, 2 drum sounds and a cymbal sound.
• The relative sample volumes are not very consistent.
• Note endings after release are abrupt cutoffs, rather than proper release fading (although the normal decay during a sounding [e.g. piano] note is handled properly).
• The strings have too long an attack time, so on some pieces the strings sound like they're being played backwards.
• The organ sample chosen was very compact, but has too little harmonic content. The result is that low frequency notes, played through the Gameboy Advance 'speaker' sound more like distortion than musical notes.
• Percussion channel is assumed to be 10 - no attempt is made to sense the channel or allow the user to change it in this version.

Release V0.9

Changes to this version

• Samples have been improved using a new app which specifies the samples and combines them at the click of a mouse. This makes trying a small change to a sample much faster.
• Samples used are Piano, Harpsichord, Sax, Church Organ, Steel Guitar, Distortion Guitar, Flute, Marimba, Trumpet, Violin, String Ensemble, Drum, Bass Drum, High Hat
• Full envelope control is now available though not much used.
• Bug fixes prevent failure caused by 'Polyphonic Key Pressure', 'Channel Pressure', 'Pitch Bend' and 'System Exclusive' messages. (Now doesn't fall over playing the example files I was sent. Don't get me wrong; I still don't handle these messages, I just ignore them correctly!)
• Fine tuned the frequencies in the loop sections.

Release V0.91

Changes to this version

• Added a further Electric Organ sample as the Church Organ didn't work with Rock.
• Implemented 'Pitch Bend' which gives big improvement on midi files which use it

Installation in Pogoshell

Get it here

• Place the midi091.bin file in your Pogoshell .plugins folder.
• Create a folder for your MIDI files and put some *.mid files into it.
• Edit the file filetypes in the .shell folder by adding the line shown in red below (all one line - even if shown wrapped below)

• Create your ROM in the usual way...