I've been looking at a number of speech codecs: CELP - As used in US cellphones LPC10 - VERY compact but low qualith ADPCM - excellent quality but bulky Now, I've come across the NATO replacement for LPC10 and it's called MELPe (Mixed excitation Linier Prediction). LPC10 works at 2400BP/s so it's small but it sounds like a vocoder (good if you want robot speech) Now, as for MELPe, a company called Compandant have taken this route even further/ 2400/1200/600 bits per second. I suspect the lower rates will suck, but I wonder what the 2400 bit version is like (better than LPC 10 in any case). Now, since this is a product that just plays back recorded speech, I assume error correction can be left out. I also wonder if, such as in CELP, the signal is generated by analysis-by-synthesis. I don't think can test every codebook, but with encoding time not an issue, is better quality speech possible? Sean
If this is for a commercial product you better make sure they don't got some stupid patent on it first.:-(
Yes, I'm aware that it is patented. Since I only need DECODE in real-time, and it could be a gateway into a new market for them (since I will code the DS, Wii (and possibly mobile phone) versions of the decoder, there maybe a deal in the offing. I gor CELP for free years back by writing the code and then giving them the rights back (you can run CELP decode on a CGB believe it or not). I just wondered if anyone knew of OTHER low bitrate codecs. I can afford up to maybe K3Bit/Second but CELP at that rate is awdul.. Thanks, Sean
CELP is, in effect, build from lookups + some coefficients. One of the limits of CELP is that it used analysis-by-synthesis during decoding. You have a number of dimentions, a number of loopups & some filter coefficients. If you can search every entry of the lookup, you should get the best result. I think in most applications they organize the lookups so that the encoder doesn't have to search all of it.
A friend on mine did a ADPCM decoder on MD using a 32KB LUT... probably the most lightweight decoder ever. In his implementation the 68K did the decoding and Z80 playback. Result is great, I don't have a link to the ROM image though...
ADPCM manages 4:1 compression (more at the cost of quality). ADPCM manages about 550 bytes per second.
