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I didn't optimize tremor with much assembly, so there's room for improvement. It handles mono at 24 to 64 kbps, but it would really need optimizing to get stereo going on it. SirenAC was better in terms of cpu load, even without optimizing. I'd like to see what you get with your assembly DCT plugged into tremor, if you can figure that out.
One thing about the branch I used - I used the low-memory branch of tremor, which has a leak in the memory handling somewhere. I didn't bother to track it down; instead, I just reinitialize the heap used for tremor memory allocation each time through. In general, without good assembly language improvements to parts like the DCT, most DCT based codecs are going to start maxing out at around 64 kbps. Emulators would go higher, but then the emulators have always exaggerated the speed of the 32X somewhat. They don't emulate some of the things that slow real hardware down, like cache line fill, bus speeds, bus collisions, etc.
BTW, I used to use FileDen, but then when they shut down, I had to move a lot of stuff over to MediaFire. I'm as surprised as you that they're still around. If you want some of my examples, just PM me and I can get you some arcs. |
I took one look at the C routine and noped right out of trying to make an SH2 assembly routine. Funny enough, I'm quite skilled at Walsh-Hadamard transforms. I keep going back and looking into a codec based on that for old consoles like the 32X/Saturn. 
Knocking the block size down from 128 samples to 64 frees up some CPU time to allow for stereo. Interleaving the processing of the second channel with the first can reuse some LUT data while it is still cached instead of hitting SDRAM again which is good too. Then I started to add huffman coding. Now the CPU is pushed right to the limit, with a few pops and skips happening in Fusion. Bitrate is still high but quality sounds good.