EA MicroTalk (also UTalk or UTK) is a linear-predictive speech codec used in various games by Electronic Arts. The earliest known game to use it is Beasts & Bumpkins (1997). The codec has a bandwidth of 11.025kHz (sampling rate 22.05kHz) and frame size of 20ms (432 samples) and only supports mono. It is typically encoded at 32 kbit/s.

Docs: http://wiki.niotso.org/UTK

In this repository, I have created a set of open source (public domain via the UNLICENSE) MicroTalk decoders/encoders.

• Use utkdecode to decode Maxis UTK (The Sims Online, SimCity 4).
• Use utkdecode-bnb to decode PT/M10 (Beasts & Bumpkins).
• Use utkdecode-fifa to decode FIFA 2001/2002 (PS2) speech samples. This tool supports regular MicroTalk and MicroTalk Revision 3 SCxl files.(*)
• Use utkencode to encode Maxis UTK. (This is the simplest container format and is currently the only one supported for encoding.)

(*) I wasn't able to find any real-world MicroTalk Rev. 3 samples in any games. However, you can transcode a FIFA MicroTalk Rev. 2 file to Rev. 3 using EA's Sound eXchange tool (sx -mt_blk input.dat -=output.dat).

gcc -Wall -Wextra -Wno-unused-function -ansi -pedantic -O2 -ffast-math -fwhole-program -g0 -s -static-libgcc -o utkdecode utkdecode.c
gcc -Wall -Wextra -Wno-unused-function -ansi -pedantic -O2 -ffast-math -fwhole-program -g0 -s -static-libgcc -o utkdecode-fifa utkdecode-fifa.c
gcc -Wall -Wextra -Wno-unused-function -ansi -pedantic -O2 -ffast-math -fwhole-program -g0 -s -static-libgcc -o utkdecode-bnb utkdecode-bnb.c
gcc -Wall -Wextra -Wno-unused-function -ansi -pedantic -O2 -ffast-math -fwhole-program -g0 -s -static-libgcc -o utkencode utkencode.c

The encoder for now is very simple. It does LPC analysis using the Levinson algorithm and transmits the entire excitation signal explicitly. Compression is achieved by choosing a large fixed codebook gain, such that each excitation sample has a large (coarse) quantization step size. Error is minimized in the excitation domain, and the quality is somewhat poor for bitrates below about 48 kbit/s.

However, MicroTalk is a multi-pulse codec (it is cheap to code long runs of zeros in the excitation signal). Hence, a much better design (and indeed the standard practice for multi-pulse speech codecs) is to search for the positions and amplitudes of n pulses such that error is minimized in the output domain (or the perceptually weighted domain). This new encoder is still in the works.