Monday, January 25, 2010

Having the audacity to play with audio speed

I have a student in my current class who told me that she simply couldn't understand the audio recordings we're using in class. That's not so unusual, but after working with her for a bit in my office, I came to believe she has an unusual disjunction between her reading ability and listening ability. So I whipped out Audacity and started playing around with the files.

There is an option to change the tempo (i.e., make it slower without changing the pitch), but it introduces an odd distortion to the voice. Instead, I found it better change the speed and then boost the pitch back up. To do this, you begin by opening your file (after you've downloaded and installed Audacity). Step 2 is to select the portion of the file you'd like to slow down. In most cases this will be the whole recording. Step 3 is to click on Effect from the menu bar, and choose change speed, perhaps by 33%. Once this completed, you need to once more click on Effect and then choose change pitch. I found the pitch needed to be boosted slightly more than the amount of the speed reduction (if you can compare those two things). So, a speed change of -33% would require a pitch boost of roughly 43%.

Here's are some samples:
-basic recording
-change tempo
-change speed
-fix pitch


Drew Ward said...

Brett, I've actually found that often the problem is not with the speed of the recording, but with the horrible acoustic qualities of most tape/cd players. The ones used form most classrooms are really designed for use outdoors or at the beach or something, and always for music.

This means they have most of their design focussed on providing good response to the bass and treble ranges, but very little for the range at which most speech occurs.

I have experimented by putting the same recordings on my computer/ipod/etc and playing them through a decent set of computer speakers or a nicer stereo and found that most students had a much better time because they weren't distracted by the nature of the playback (which on the portables sounds about like a Charlie Brown adult -- wah wah wawa wah).

Brett said...

Good point Drew! In fact, the MP3 files are all available to the students who can use whatever listening device they want. I haven't used a CD or cassette player in class for years.

Q Higuchi said...

I do like the program (Audacity), too. For EFL purposes, however, I usually use QuickTime 7 (free, I believe) to slow down without changing pitch. You open a file, and go to 'A/V Control' where you can make it slower, faster, even go backwards.
I am using a Mac, but I believe there is a Windows version as well.

And yes, sound quality matters. I am grateful to the admin people at my workplaces for putting up with my yearly request/demand for better A/V equipment ...