Impulse Filter vs Manual Interpolation

[Marcus]

I'm starting to think about my next restoration/archiving project. The project I am working on now is from an audio cassette source, so manual interpolation has been useful in fixing dropouts, short phasing sounds, etc. I used to have a version of DCart many years ago and used it to transfer some records to my PC. I used the filters exclusively to fix any pops/clicks, but I don't recall ever using manual interpolation. I'm not sure if it wasn't a feature or I just didn't know about it.

Anyway, my question is whether the filter is the same thing as interpolation automatically carried out, or is there more to the filter than that. I tend to use the filters as lightly as possible, and as specifically as possible. So if I hear a click, I select the area then start working with the filter to eliminate it, but you have to play with the settings a lot to find a setting that doesn't alter the sound as well. If I could just zoom in, select the click precisely and hit the I key, that would be very useful to me as I tend to target specific instances of audible clicks/noise, but as I said, I'm not sure if the filter is doing something that interpolate is not doing.

[Craig Maier]

I am not sure when we incorporated the manual interpolator into the product, but it was a long time ago (15 years?). The interpolation algorithm has been improved over the years and uses both time and frequency domain techniques to repair the gap. Different impulse filters use different replacement algorithms. Always use the EZ Impulse filter, not the expert impulse filter. The latter is intended for use in Forensics applications primarily. For example, the EZ impulse filter actually includes 3 (or 4 when big clicks are checked) detectors and replacement routines. The manual interpolator can handle longer events than the automatic impulse filters (scratch, crackle, narrow crackle and big click). And, there are two manual interpolation routines available to you. The I key (interpolator) handles longer replacements, but the O key (oterpolator) sometimes works better on very short replacements than the I key and vise versa. The EZ impulse filter is just a system to provide automatic de-clicking. Running it very lightly several times on a file produces better results than on pass with high settings. I have three EZ impulse filters set up in the multifilter that I use for eliminating impulse noise with each one set quite light in there settings (around 30/30/40).

Craig

[Marcus]

If you have a relatively clean record with some specific areas of concern, is it ok to just highlight those areas and run the EZ filter in those sections or is it best to run on the whole file? Didn't know the expert filter was meant for forensics, thanks for that info.

[Craig Maier]

Yes, I do often use the EZ Impulse filter selectively on a file. It works quite well that way, but takes a little more time to accomplish the task,

Craig

[Marcus]

I'd rather spend the time and get it right. Although I'm sure the filters won't harm audio if used correctly, I feel it's safer to apply it first, where it's need and second, as you said in layers. Maybe it just makes me feel better in the end though.

Thank for your patience if I'm asking silly questions as well, you've been very helpful.

Oh, and I remembered where I obtained my first copy of DCart. It came packaged with an Imation CD-RW. Probably around the year 2000.

[Craig Maier]

Ok - I vaguely recall those days (bundling). I tend to use the EZ Impulse filter selectively especially on musical material that has a wide dynamic range. Classical music is an extreme example of that. In that way, I can use the filter(s) more aggressively on the soft passages and less aggressively on loud passages. Loud passages tend to 'mask' noise anyway, so it works out well for me when used in that manner.

Craig