Speech Processing by Computer
LAB 1
EDITING
OF SPEECH SIGNALS
This lab session
demonstrates the effect of choice of sampling rate and quantisation on the
quality of a digitised speech signal.
The effects of 'aliasing' distortion arising from sampling at too low a
rate are heard. The use of SFS programs
for editing signals is explored.
1. Choice
of sampling rate
(i) Acquire a speech signal at 20000
samples/second.
(ii) Use the Tools/Speech/Process/Resample
command to resample the signal at 16000, then 12000, then 8000 samples per
second.
(iii) Listen to the four versions. How do they differ? Why?
2. Choice
of quantisation level
(i) Acquire a speech signal at 20000
samples/second.
(ii) Run the program 'qchange' and enter the
name of your speech file.
(iii) Select the number of bits of quantisation
(from 16 downto 1) and listen to the replayed version. What happens? Why?
3. Aliasing
distortion
(i) Acquire a speech signal at 20000
samples/second.
(ii) Run the program 'rchange' and enter the
name of your speech file.
(iii) Select a new sampling rate between 6000
and 20000 and listen to the replayed version.
What happens? Why? What is the difference between what
'rchange' does and proper resampling?
4. Editing
(i) Acquire into separate files the
utterances:
"The
time is" into file
't1.sfs'
"ten" into file 't2.sfs'
"minutes
past" into file
't3.sfs'
"twelve" into file 't4.sfs'
(ii) Using the Tools/Speech/Edit command,
select annotation mode with annotation labels of type ‘marker’. Add markers
into the files indicating where the speech signal starts and stops in each
file. Use the markers 'start' and
'stop'.
(iii) Using the ‘notepad’ editor, create a text
file 'time.txt' containing:
t1.sfs,,,start,stop
t2.sfs,,,start,stop
t3.sfs,,,start,stop
t4.sfs,,,start,stop
(iv) Create
a new empty SFS file
(v) Run the program Tools/Generate/Concatenate signals to edit the component parts together
(vi) Replay the concatenated signal. What are the problems with your concatenated utterance? How might it be improved?
(vii) Change your files to make the utterance
'The time is twelve minutes past ten'.