Newbie question - impulse filter on selection

[Peter Allen]

OK - I am an absolute beginner using Millennium 4.80, and have to be doing something silly here.

I have been using the manual interpolate method for single click removal with no problems.

Now I come to a click that I cannot locate by eye. So I used File Conversion to produce a destination file, then selected the region containing the click in the source file, and opened the Impulse Filter.

In preview mode the offending click was removed with the default setting - raising the tracking level failed to remove the click, and lowering it started removing music. So default settings it was.

I ran the filter on the source file selection. Playing back the destination file shows the offending click eliminated, but two small clicks added at points corresponding to the beginning and end of the source file selection.

What am I doing wrong?

Humble thanks in advance,
Peter

[Craig Maier]

Re: Newbie question - impulse filter on selection

I do not think that you are doing something wrong. However, if the highlighted section of the source file is real small, you will probably run into the transient response recovery time of some of the filters within the impulse filter proper. As a result, it itself can produce output transients. Try selecting a longer interval and see if this solves the problem. Or, as an alternative, use the high pass filter on the file to make a destination file. This will make the clicks easier to view in the destination file. Then simply use the manual interpolate function on the source file wherever you see clicks. Set the high pass for a few KHz.

[Peter Allen]

Re: Newbie question - impulse filter on selection

Craig, thanks for that filtering hint to help identify clicks by eye.

However, your comment about the width of the highlighted section doesn't seem to explain the introduction of artefact clicks by the impulse filter.

When I chose the section of the file on which to run the filter, I deliberately widened out the selection to 3 seconds, thinking along the same lines as you, ie wanting to operate on as small a selection as possible for a localized problem, but not so small as to cramp the filter's style in the problem area. I would have thought the filter should know how to ignore the selection boundary.

I have just pulled the original file out again and repeated the exercise with a selection width of 80 seconds running from the beginning of the file to 65 seconds after the event to be removed.

I still get a filter-generated click in the destination file at the position of the source file's second selection boundary.

I have kept a screen shot of the artefact this time.

Obviously I can manually remove the impulse filter's artefact, but that doubles the length of the job. The question remains as to why the artefact is there in the first place, and whether I should be doing anything differently to avoid it.

Peter

[odass]

Re: Newbie question - impulse filter on selection

I am also having this problem. When I run the Impulse noise filter on a portion of a source file, an artifact is always introduced in the destination file at the location coresponding to the very end of the selected portion. Sometimes the artifact is hardly recognisable, audibly or visually, while other times it looks/sounds like a big spike/heavy click. The artifact is very short in duration, so it is easily removed through the paste interpolate function.

I am working very much on early low quality acoustical recordings, and I spend 2-3 hours declicking a three minute file. All the time I use selective filtering on small portions with different filter settings, in order to get optimal results. As I always have to zoom in on the end of a filtered portion to check for artifacts, it really increases the work.

I have had this problem on all versions, so I am quite sure it must be a bug, and it would really be a relieve to see it fixed.

Terje

[Peter Allen]

Re: Newbie question - impulse filter on selection

Thanks Terje.

Craig, is it possible for you to confirm that this is a bug in the program?

All that is required is for the Impulse Filter to be applied to a selection of any audio file, using the default parameters, followed by close visual inspection for distortions of the destination file at the selection boundaries.

Peter

[Rick]

Re: Newbie question - impulse filter on selection

Well it is part bug, part filter settling. There are two blips at the start and end of the selected area. The one at the start is caused by the filters impulse response, and can be greatly reduced by moving the start of the selected area to a zero crossing in the waveform. The glitch at the end of the selected area can also be reduced by moving the end of the selected area to a zero crossing in the waveform, but it is a bug. The filter does not empty out correctly at the end of the selection, leaving a glitch. Both of these problems will be fixed in the new version.

Rick Carlson

[quartet87]

Re: Newbie question - impulse filter on selection

I've encountered a similar sympton at the end of files after running file chop. There's usually a loud pop at the end of each chopped file except for the end of the file which was the tail of the source file. Same thing?

Danny Gilbert

[Rick]

Re: Newbie question - impulse filter on selection

No, I do not think so. There are no filters running when a file is chopped, it is simply copied from one file to another. It could be that the chops do not occur at zero crossing, which means that you would be doing the chopping in the middle of some music. There could also be some DC offset in the file which would cause a pop when it went away and would occur even at the end of a file where there was silence.

Rick Carlson

[Peter Allen]

Re: Newbie question - impulse filter on selection

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by rickc:
Well it is part bug, part filter settling.
{SNIP}
Both of these problems will be fixed in the new version.

Rick Carlson<HR></BLOCKQUOTE>

Thanks Rick, that is good news.

Peter