Although it contradicts nocash docs, Spyro 2 (PAL) uses 0x21.
Should only 0xff be rejected?
                        subhdr->file, subhdr->chan, cdr.CurFile, cdr.CurChannel, cdr.FilterFile, cdr.FilterChannel);
                if ((cdr.Mode & MODE_SF) && (subhdr->file != cdr.FilterFile || subhdr->chan != cdr.FilterChannel))
                        break;
-               if (subhdr->chan & 0xe0) { // ?
+               if (subhdr->chan & 0x80) { // ?
                        if (subhdr->chan != 0xff)
                                log_unhandled("adpcm %d:%d\n", subhdr->file, subhdr->chan);
                        break;