Amplitude Modulation

1. Open the Sonic Foundry Amplitude Modulation dialog.

2. Choose a preset from the Name drop-down list, or adjust the controls as desired:

3. a. Drag the Dry out fader to set the level of the unprocessed signal that will be mixed into the output.

4. b. Drag the Wet out fader to set the level of the modulated signal that will be mixed into the output.

5. c. Drag the Amplitude fader to set the minimum gain of the modulated signal.

6. d. Adjust the graph as desired.

7. e. Drag the Mod freq. slider to specify the frequency of the gain waveform that will be applied to the input signal. To achieve a slow tremolo, use a low frequency.

As frequencies exceed 20 Hz, modulation is audible not as a change in amplitude, but as additional frequency side bands.

The amplitude graph represents the gain that will be applied to the input signal over time. The vertical line should be used as a guide to center the period, and the horizontal line represents the middle of the modulating range. You can edit the gain waveform by adding and adjusting points.

• Drag the small boxes (envelope points) up or down. When the envelope is below 0 dB, the signal is attenuated.

• To create a new envelope point, left-click on any point of the envelope.

• To delete an envelope point, single-click it with the right mouse button, or double-click it with the left mouse button.

• To move all envelope points, press Ctrl+A and drag when the envelope has focus (the cursor will be displayed as a ).

• Click the Reset button to reset the graph.

Because the envelope represents a signal that is repeated at the specified frequency, clicks are likely to occur when the envelope's start and end points do not line up. If you are sure you have drawn the period correctly and still hear transition clicks, select the Blend graph edges check box to apply an edge-smoothing algorithm that will help eliminate the clicks.

Drag the Stereo pan slider to offset the phase of the two channels' amplitude gain envelopes by the specified percentage. This creates a back-and-forth panning effect between the two channels.

Panning is only available for stereo files.

You can apply a low-pass filter to tailor the high-frequency content in your processed signal.

Select the Low-pass start freq. check box and drag the slider if you want to filter high frequencies. Move the slider to the left to filter more high-frequency material and to the right to leave more high-frequency material. The results are a brighter or more muted sound.