MUSC 108. Introduction to Music Technology - Fall 2013

11 Lab 2 - Digital Audio Gotcha 1 - Clipping

Open A New Audacity Window

Create a 200 Hz Sine wave with an amplitude of 1 and a duration of one second.

Add 5 New Audio Tracks

Select Track 1 and Copy

Select Track 2 and Paste

Paste Into All Remaining Tracks

Select All Six Tracks and Mix Down to One Track

Hint: Hold down the Shift key when you click in the Track Control Panel.

Then choose Mix and Render from the Tracks menu.

Zoom in on the Mix Wave

Notice the flat tops on the Mix track. That's the sign of clipping. When you mixed thesine waves together the amplitudes of the individual waves were add together. Our Mix wave became a sine wave with amplitude 6.0. Audacity cut off the tops and bottoms of the mix wave to fit into an amplitude of 1.

Add a New Audio Track with the Initial 200 Hz Sine Wave

Solo the Mix wave and play it.

Solo the Sine wave and play it.

You should hear a distinct difference between them.

Clipping in the Mix wave results in distortion, the "buzzy" part of the tone.

Compare the Spectrum of the Two Waves

Select the Mix wave and choose Plot Spectrum from the Analyze menu.

Select the Sine wave and choose Plot Spectrum from the Analyze menu.

You can see the extra noise.

Repeat the Procedure To Eliminate Clipping

This time generate the sine wave with an amplitude of 0.15. When the six amplitudes are summed, the total amplitude will be under 1.0.

Paste Into Six Tracks

Mix and Render

Because the total amplitude remained under 1.0 there is no clipping.

Continue with 11Lab3.

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