1) Problem.
- Preparing a live recording for presentation may require the removal of clapping from the nearby audience.
- Using a frequency or amplitude filter to automatically remove the clapping would be a preferred method as one of the steps in preparation of the material.
- But creating a filter involves understanding the clap waveform and how it mixes with the other wav file contents.
- The following steps describe the investigation of removal of clapping by analyzing the clap waveform.
2)What does a clap look like?
- As the expanded picture shows a high initial amplitude excursion at a high frequency.
- The signal amplitude decays rapidly, but the ringing will last for 10 times longer.
- The time line shows that the initial clap is short.
- The ringing portion of the waveform is due to the room size and will vary according to the recording location.
3)Examine the Frequency Spectrum of the clap
- The frequency spectrum of the clap shows that the energy is broadband from 0 to 20 KHz.
- Creating a filter would require the whole audio band to be removed to eliminate the clap.
4)Mix Clap +1kHz
- The clap waveform is mixed with a lower level 1KHz waveform.
- The initial amplitude and frequency is much greater than the 1 Khz tone; the cycles are much closer together.
- As the clap decays it rides on top of the 1KHz tone.
- For selection of the clap a few cycles of 1KHz before the initial amplitude spike to a cycle of 1KHZ that has little clap modulated onto it.
5)Examine the clap waveform in the source material
- Scroll through the area to be edited and locate a clap.
- For selection, zoom in on the clap so that it fills the screen.
6)Select the clap waveform for editing
- Start the edit on the zero crossing of the underlying waveform in that area.
- When selecting the area to be edited, also include at least one cycle before and after the clap to provide area for the crossfade.
7)Crossfade the edges of the edit
- This crossfade will extend the left section of the file area into what was edited out.
- The cross fade decreases the volume of the left hand part of the file as it increases the right hand part of the file.
- Select the edit to start one cycle before the clap starts.
- Select the edit to finish one cycle after the clap finishes.
- Remnants of the clap end not edited out will sound like a dull pop.
- The area removed including the extra two cycles wil not increase the overall edited length by a noticable amount.
