MUSC 108. Introduction to Music Technology - Fall 2013

11 Lab3 - Digital Audio Gotcha 2 - Clicks

Open A New Audacity Window

Create a 200 Hz Sine wave with an amplitude of 1 and a duration of 250 Milliseconds.

Extend the Sine Wave

Copy the entire 250 ms of the sine wave.

Click the Skip To End button to position the cursor at the end of the track and paste.

Shortuct: Right Arrow key.

Repeat the paste two more times and click the Fit Project button.

You should see one minute of sound.

Play

Rewind to the beginning and click the Play button.

You should hear four distinct clicks.

Select a Small Section On Both Sides of a Paste Boundary

Click the Fit Selection Tool

There is a discontinuity at 0.2500. Discontinuites are heard as clicks.

These are three more example illustrations of a discontinuity.

And the Solution Is...

...Always Copy and Paste on Zero Crossings

Select all the audio in the track by clicking once in the Track Control Panel and then delete the audio.

Generate the 330 Hz sine wave again so there are 250 ms of audio in the track.

Find Zero Crossings

Make sure all the audio is selected and choose Find Zero Crossings from the Edit menu.

Shortcut: Type Z

You notice that all of the waveform has been selected except for a small portion at the right edge.

Copy the selection and then delete all audio on the track.

Rewind to the beginning and Paste. The audio will now end on a zero crossing.

Extend the audio to one minute by pasting three more times.

Play

This time there should be no clicks.

Close Up of Find Zero Crossings

Selection Before Find Zero Crossings

Selection After Find Zero Crossings (Type Z)

Try it.

Continue with 11Lab4

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