How I got cmusphinx's transcript alignment tool to work.
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cmusphinx forced alignment example

So... building cmusphinx isn't exactly easy and running its forced alignment tool isn't well documented. (Forced alignment is matching a transcript with corresponding audio and getting time codes for each word in the transcript.)

This project documents how I got cmusphinx (the latest development version) working on an Ubuntu 14.04 x64 machine to work. Version 4-5prealpha had some sort of bug in the aligner. The latest development version has a broken build which I fixed manually by reverting this commit manually.


Build Sphinx4, which is a Java library:

sudo apt-get update
sudo apt-get install git default-jdk maven

git clone
cd sphinx4/sphinx4-core
git revert aa4e1838f06eb032fd248601469b16ac95aeb08a
mvn clean install
cd ../..


You'll need an acoustic model. Here I'm using English:

tar -zxf cmusphinx-en-us-5.2.tar.gz


To test that this all worked so far, try out forced alignment with a sample 16khz 16bit mono wav file (it must be in that format). First get the file and its transcription:

wget -O sample_original.wav
sox sample_original.wav -b 16 sample.wav channels 1 rate 16k
echo "It's a dense crowd in two distinct ways. The fruit of a figg tree is apple shaped." > sample.txt

Then run cmusphinx's aligner program:

java -cp sphinx4/sphinx4-core/target/sphinx4-core-1.0-SNAPSHOT.jar cmusphinx-en-us-5.2/ sphinx4-5prealpha-src/sphinx4-data/src/main/resources/edu/cmu/sphinx/models/en-us/cmudict-en-us.dict sample.wav "$(cat sample.txt)"

It's going to write out a whole bunch of new wav files (in this example just sample-0000.wav) --- be on the lookout for those generated files.

Better Driver

My driver class simplifies things. It takes a filename for the transcript on the command line rather than the transcript text directly, and it outputs the alignment in CSV format. Get the opencsv library and then compile my driver class:

javac -cp sphinx4/sphinx4-core/target/sphinx4-core-1.0-SNAPSHOT.jar:opencsv-3.3.jar 

And run the same example with my driver:

java -cp .:sphinx4/sphinx4-core/target/sphinx4-core-1.0-SNAPSHOT.jar:opencsv-3.3.jar Aligner cmusphinx-en-us-5.2/ sphinx4-5prealpha-src/sphinx4-data/src/main/resources/edu/cmu/sphinx/models/en-us/cmudict-en-us.dict sample.wav sample.txt 2>/dev/null

Or just:

./ sample.wav sample.txt 2>/dev/null

You'll get:

"it's","IH T S","false","0.0","170","200"
"crowd","K R AW D","false","-1.13934288E8","850","1300"
"in","IH N","false","-1.95127088E8","1300","1470"
"two","T UW","false","-2.23176048E8","1470","1700"
"distinct","D IH S T IH NG K T","false","-2.6345264E8","1700","2230"
"ways","W EY Z","false","-3.58427808E8","2230","2730"
"the","DH AH","false","-4.72551168E8","2920","3100"
"fruit","F R UW T","false","-5.24233504E8","3220","3530"
"of","AH V","false","-5.79971456E8","3530","3640"
"figg","F IH G","false","-6.2017152E8","3760","4060"
"tree","T R IY","false","-6.72126656E8","4060","4490"
"is","IH Z","false","-7.4763744E8","4490","4570"
"apple","AE P AH L","false","-7.73581184E8","4630","5040"
"shaped","SH EY P T","false","-8.44424704E8","5040","5340"

My driver outputs a CSV table, to standard output (you can redirect it to a file if needed), with columns:

  • the word (as it appeared in the transcript)
  • the phonemic prounciation of the word (from the dictionary)
  • whether this word was a filler (automatically inserted?)
  • the confidence of this word's alignment (not sure if higher is better...)
  • the start time of the word, in miliseconds
  • the end time of the word, in miliseconds


sphinxbase, the native C portion of cmusphinx, isn't required for this. I didn't know that ahead of time (thanks cmusphinx!), so I'm pasting build instructions here but you don't need this:

sudo apt-get install bison swig python-dev 
tar -zxf sphinxbase-5prealpha.tar.gz
cd sphinxbase-5prealpha
sudo make install
cd ..