Unformatted text preview: ailor the effects of the process to work better for
specific source material. Learning how to modify the envelope points takes practice, but can
lead to achieving better results.
After you have captured the noiseprint, the frequency spectrum of the noise is displayed,
along with envelope points outlining the noise model the algorithm with use. NOISE REDUCTION CHP. 2 19 Changing the fit size
The Fit size determines how many envelope points are created after capturing the noiseprint.
In general, using a large number of envelope points is recommended; as you use more
envelope points, the Noise Reduction algorithm can work more precisely to reduce noise.
You may want to use a smaller Fit size if you plan to manually modify the envelope points. To change the Fit size value, you may click the up and down arrows to the right of the edit
box or type a value in the box. If you change the Fit size value, click the
generate new envelope points. Manually adjusting envelope points
The envelope points above the noiseprint indicate the amplitude threshold below which the
Noise Reduction algorithm operates. This means that for most applications, the envelope
should be slightly above the noiseprint.
The envelope points can all be raised or lowered by using the Envelope amplitude control. If you raise the points too high, it is likely that you will remove part of the source material
and generate flange-like artifacts. If the points are too close to the noiseprint, some of the
noise may not be removed.
It is important to remember that for the noise to be removed, the envelope contour must be
above the noiseprint. CHP. 2 NOISE REDUCTION 20 The Noise bias control achieves similar results as manually modifying envelope points. For some applications it may be necessary to move individual or groups of envelope points.
For example, if your source material has a lot of frequency content in common with the
noise, reduce the noise only in the places with little overlap: common with speech and tapehiss noise.
Moving one envelope point To move an individual point, click and drag one of the square envelope handles. Move one envelope point Moving a group of envelope points To move a group of points, click and drag a box around the envelope points you want to
select. (If you see the magnifying glass icon, right-click until you see the cross hairs icon.)
Selected envelope points will appear in red. After you have selected a group of points, you
may click and drag the entire group. Move a group of envelope points NOISE REDUCTION CHP. 2 21 Affecting frequencies with envelope points You may use envelope points to eliminate high-frequency noise and preserve the lowfrequency portion of the audio by doing the following:
1. Select all of the envelope points below 1000 Hz. Unaffected frequencies 2. Drag the points down so that Noise Reduction will not affect those frequencies. Or, to ensure that high frequencies will be attenuated, raise the envelope points above the
cutoff frequency. Cutoff frequency Frequencies being attenuated Note: If the envelope point is below the
noiseprint level, the audio at that frequency
will not be affected. Conversely, if the
envelope point is above the noiseprint level, the
audio at that frequency will always be reduced
by the Reduce noise by slider setting. Resetting and fitting envelope points At any time, you may reset the envelope to its default position by clicking the
button again will reapply the envelope to the current noiseprint.
CHP. 2 NOISE REDUCTION 22 Zooming into the noiseprint
When making manual adjustments to the envelope, it is usually necessary to zoom into the
graph to better see what frequencies you will be affecting.
Zooming can be accomplished in several ways:
• Click on the noiseprint graph and draw a box around the area you wish to zoom. With
that area selected, right-click on the noiseprint graph to display a pop-up menu. From the
pop-up menu, choose Zoom Selection. Only those points should be visible. Change the selection type in the noiseprint graph. The normal type is to select points, but
by right clicking while holding down the left mouse button, you can toggle the selection
types and three different zoom types.
• The first type is a vertical zoom window. This type allows you to zoom into a specific level
range of the noiseprint. • The second type is horizontal zoom window. This type allows you to zoom into a specific
frequency range of the noiseprint. NOISE REDUCTION CHP. 2 23 • The third type is a combination of vertical and horizontal zoom. It functions in much the
same way as the selection mode. This type allows you to zoom into a very specific
frequency and amplitude range of the noiseprint. To return to the selection mode, toggle the cursor until it becomes a cross hairs.
You can use Grab/Pan mode to scroll the noiseprint graph at the current magnification. This
is useful for navigating through the noiseprint while zoomed in at a high zoom factor.
To switch into Grab/Pan mode, right click the noiseprint and choose Grab/Pa...
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- Winter '10