A FAT32-formatted microSD card is required for impulse upload.
When the microSD card is used for the first time, an AFX folder with stock impulse files is automatically created on it. The files are stored in subfolders corresponding to the CABINET knob positions. To use custom impulses, replace the stock files with your own. Impulse format: .wav mono 24bit 48kHz WAVE PCM1, uncompressed.
Impulse length: 940 samples (19.58ms). You can upload longer impulses but only the first 940 samples will be used.
To re-record the stock impulse files to a microSD card, insert a blank card into the device. This will automatically create an AFX folder and all its contents. If there is no card in the microSD slot, the stock impulses (stored in the device's memory) are used.
To learn more about using the microSD card, visit the Support Page