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EchoCancel

EchoCancel is the process of removing echos from audio in order to improve the quality. Echo cancel may be needed because an audio recording was done in a room that led to echo generation or there was some kind of unwanted feedback. There are many controls for the EchoCancel plugin which are defined here. However, the first thing you will see when you bring up the plugin, is the top portion that is black which will show a + in the middle when you mouse over it. Once you start playing audio, you will see the cepstrum spectral data inside the window. A cepstrum results from taking the inverse Fourier transform (IFT) of the logarithm of the estimated spectrum of a signal. It is used to identify the period of the echo in the audio. It is recommended to just set the Mode to On but the below defined parameters can be utilized by professionals (figure 10.18).

Figure 10.18: GUI for EchoCancel with crosshair and mode set to ON

Normalize:
  audio normalization adds variable amounts of gain to an audio recording to bring the average or peak amplitude to a target level (the normal amount), on an ongoing buffer by buffer basis. This is to make the cepstrum graphical data appear between 0 and 1. Checkmark appears if ON.
Level:
  scale factor used to draw the cepstrum output when normalize is not in effect.
History:
  number of previous cepstrum outputs redrawn as fading graphical data.
X Zoom:
  X axis scale factor to magnify low frequency cepstrum graphical output.
Damp:
  echo envelope decay factor used to smooth the cepstrum/correlation data.
Peaks:
  number of maximal envelope values used in the echo gain calculation.
Cutoff Hz:
  low frequency cutoff value to prevent beat frequency (heterodyne) echo canceling.
Mode:
  MAN, Off, or On. When Off is selected, the plugin is not active. When MAN is used, the only one peak is used for the echo gain envelope. It is set by pressing mouse button 1 (LMB) in the ceptstrum graphical output. The Gain and Offset are updated as the pointer drag operation resets the indicated gain and offset values. When On is selected, the echo gain envelope is automatically calculated by cepstrum and auto-correlation of the input audio in the last window size audio samples.
Windows size:
  parameter can be set to Default, 1024, 2048, ...doubled values... up to 262144.
Amplitude:
  the cepstrum value at the drag point during manual envelope selection.
Gain:
  echo gain setting determined by manual selection.
Offset:
  echo period setting determined by manual selection. The Hz (frequency), ms (millisecond duration), and sample offset (audio samples) as determined by manual selection.