For those of you interested in trying to get more than 8 stereo voices, there is a so-far undocumented init file command that will let you experiment with more. “#VOIC n”, where n is desired number of voices, allows you to increase the number up to a maximum of 16. You’ll need to add this command to an existing init file using a text editor, since the WT-InitMaker app does not support it. You can confirm the setting using the WT-Remote app – the “Get Info” button reports the number of available stereo voices.
In most cases, it’s probably safe to increase the number of voices to at least 10. 8 was chosen as the default to be compatible with the slowest microSD card I’ve encountered. Without a scope, you’ll know when you’ve hit the limit for your card when you start to hear crackling or pops after layering the max number of tracks. For those of you with a scope, PC15 (pin 4 on the STM32F4) duty cycle indicates the amount of time taken by the mixer. 100% is bad.
The limiting factor for the number of voices is what I call the “access time” of the microSD media, which is different than the sustained bitrate used for the speed ratings. Unlike sequentially reading a single file, mixing WAV tracks involves reading a small number of sectors from files spread all over the FAT disk. The critical issue is the time it takes between asking for a new sector read and when the card actually starts providing that data. I’ve not found this parameter to be documented by the microSD card manufacturers, so you’ll just have to experiment with it.