All cards should have a speed class of 4 or higher, and we strongly recommend SanDisk cards, though PNY and Kingston cards will also work.
The SM2 series of recorders was produced prior to the introduction of the SDXC card standard, which raised the maximum size of an SD Card from 32 GB to 2048 GB. Using SDHC cards, with a maximum size of 32 GB, is the most reliable option when using an SM2, as using SDXC cards can lead to dropped audio and unreliable file transference.
SM3 & SM4 Series
The SM3 and SM4 lines of recorders support both the SDHC and SDXC card standards, meaning they can use cards up to 2048 GB in size.