AI, which is not always 100% accurate, makes these observations...
"The best export format from NCH MixPad for upload to SoundCloud is WAV, FLAC, or AIFF for the highest audio quality, as SoundCloud recommends lossless HD formats for uploads. However, MixPad also allows exporting as MP3, which is accepted by SoundCloud and is often sufficient for many users—choose at least 320 kbps MP3 if using this format.
To ensure the highest compatibility and audio quality on SoundCloud, select WAV or FLAC as the export format in MixPad's export options. For file size considerations, 16-bit WAV or FLAC is generally recommended."