Time Compression Recorder

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jimandy
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Time Compression Recorder

Post by jimandy » Mon Jan 07, 2008 2:59 pm

I have a project that requires a time compression recorder, essentially a voice activated recorder but the pause-recording delay value following silence can be set to a minimal, almost negligible value. The result on playback is speech that is intelligible but compressed in time. This can probably be done in software but I can’t find an app that does this (preferably for Mac OSX). Suggestions?
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VIRAND
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Post by VIRAND » Sat Jan 12, 2008 8:14 am

It looks to me like you want a faster response to voice and
faster playback at normal tones that don't sound like "the chipmunks".

You can record past time, such as the beginning of a sound
which happened before you pressed record, with a regular delay
of several seconds on the input which is always on and ready to
be recorded from. The delay would work similar to the following
effect but only use one pointer. (It can be done analogly with a
"tape loop" if you have such 'ancient' recording technology handy).

You can playback at double speed normal pitch by using a circular
delay buffer and reading it out to the speaker at half the speed of
reading it in, using two different pointers in the circular buffer.

The 2 paragraphs above describe how the program would work.

I don't know of a common software app or device that uses these
features together in some way, although many audio editing software
has a "change tempo preserve pitch" feature.

jimandy
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Post by jimandy » Sun Jan 13, 2008 1:57 pm

I think such a system is used in the production of commercials, especially for the disclaimer tags at the end where they squeeze in a minutes worth of speech into 15 seconds. Also, I recall Rush Limbaugh got bent out of shape because some of the stations that carried his radio show on a taped basis compressed the material so they could squeeze in more commercials. His beef was that he intentionally had long dramatic pauses in his monologue and editing them out made it less effective.
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dr_when
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Post by dr_when » Mon Jan 14, 2008 6:13 am

I believe there is a technology, quite old now but appears on many hand held tape recorders called VSC or something like that for Variable Speech Compression. An IC was invented by a company of the same acronym and allowed a person to "speed listen" to voice recordings assuming the IC was built into the recorder. You could almost half the playback time and still have the voice intelligible. Using pitch control and speed control. You would first adjust the playback to sound like the chipmonks and then adjust the pitch control to make the sound understandable. I have used it for audiobooks to shorten the listening time. Takes a little getting used to. Also, audio editors like the old "Cool Edit" let you make the same pitch/speed adjustments for shortening your own audio books.
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DougA
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Software ?

Post by DougA » Mon Jan 14, 2008 12:38 pm

If you want to consider a software solution, I've found GoldWave very useful. It has a "space remover" that you can control the minimum length of the space. For example, you can set .5 sec, and any space longer than .5 sec is compressed to .5. Both time and sound level are adjustable.
I also use TotalRecorder. I think it has a similar feature, but it's active at the time of recording, rather than post process.
Those are windows programs, don't know if they have a Mac version.

Your original post didn't sound like you wanted to "speed up" the playback, but if you do, GoldWave can do that too.

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Re: Time Compression Recorder

Post by DougA » Tue Jan 29, 2008 11:25 am

jimandy wrote:I have a project that requires a time compression recorder, essentially a voice activated recorder but the pause-recording delay value following silence can be set to a minimal, almost negligible value. The result on playback is speech that is intelligible but compressed in time. This can probably be done in software but I can’t find an app that does this (preferably for Mac OSX). Suggestions?
In my last post i mentioned GoldWave, I've since discovered that GoldWave has exactly what you're asking for ... voice activated, time compression recording.

In the record section, you can choose "Level activated", then set the level to trigger on, also, there is control of buffer before and after the trigger point. It can even save time cues (haven't tried that)
I used it copy a casette tape, "started" recording, went to the tape deck and started that. When the audio began, the recording began. I then discovered that it stopped recording during the dead spot when the tape reverses to side 2. As well as when the tape was finished. No editing needed.

jimandy
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Post by jimandy » Thu Jan 31, 2008 10:12 am

Thanks DougA.

As mentioned in my original post I was looking for something for my Mac. I revisited the web site for Audacity, a free audio editing program available for Windows, Mac and Linux and found they have a beta version with a feature called "Truncate Silence" which works perfectly for my application.
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