I'm entertaining the idea of making a music-creating application. I'm a total newb at signal processing. The question that concerns me most right now is, if I apply a filter/effect such as convolution, echo or reverb, flanging, etc. to only a part of a song (starting at a certain time and ending at a certain time within the span of the song), will I end up with glitch artifacts in the sound where the filter comes into and goes out of effect?

Even though I don't know much about DSP, it seems like I would, unless I were a mathematical genius and knew how to eliminate them with precision. Is this an issue, and if so, what are the ways to circumvent it? Maybe one would have to apply the filter to the entire song and change some modulating variable in the filter so that it applies the effect at zero percent at the times it's not supposed to be in effect?


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    $\begingroup$ I think your question interesting, but too general to get a proper answer. Do you have a specific audio signal you want to work on ? a specific kind of filter ? $\endgroup$ – MaximGi Feb 19 '16 at 16:39
  • $\begingroup$ or just fade it in and out of the mix. depends on what you want to do specifically $\endgroup$ – endolith Feb 19 '16 at 16:56
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    $\begingroup$ we call this "punch-in". it's a crossfade from "dry" to "wet" and at the end another crossfade from "wet" to "dry". $\endgroup$ – robert bristow-johnson Feb 19 '16 at 18:22
  • $\begingroup$ Thanks guys. I guess a crossfade/"punch-in" is the way to go. @MaximGi the audio signal would be any sound a user of the program wants to include in the track, probably soundfont2 instruments modulated by midi or something like that. For filters, there may be dozens the application would ideally support, possibly in addition to custom filters that can be coded by the user. some examples of types of filters that immediately come to mind are echo, reverb, flang, convolution by some arbitrary signal, tremolo.. $\endgroup$ – inhahe Feb 19 '16 at 21:06

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