Deleting Loud Pops in Audio Tape to MP3 Files

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Stensvaag

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I am working with a new method to convert books on audio tape to bookmarkable iPod files, by using the Radio Your Way LX device with a line-in from a simple audio tape player, the Sony TCM-929 Pressman Desktop Cassette Recorder. So far so good. This is an elegant and easy way to create MP3 files from audio tape books without having to use the PC.

Unfortunately, for reasons that elude me, I am getting loud spikes in the MP3 file (I think people in the know call these "clicks" or "pops"). I can use Audacity software to laboriously cut out each of these spurious spikes in the file, but that is time-consuming. Here is my question:

When viewed in Audacity (or any other WAV/MP3 audio file editor), the book on tape has an image pattern showing the spoken words that varies a certain distance up and down from the horizontal line in the middle of the editing screen. The clicks or pops are WAY different, being depicted by vertical lines running from the very top of the editing screen to the bottom. I wonder whether there is some command in some audio editing software which would simply let the user shear off the extraordinarily high/low ends of these vertical line spikes on the editing screen; in other words, I don't care if the click or pop is there, as long as it is not so horrendously loud that it bangs in my ears when I am using my Etymotic in-ear headphones. You could almost picture the user slicing off the top and bottom portions of ANY sound that extends more than a certain distance up/down from the center line of the editing screen.

Am I nuts? The Noise Reduction filter in Audacity seems poorly suited to this, and the Noise, Click, and Crackle filters in PolderBits Sound Editor don't seem to work either.

Thanks for any help you can provide
 
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david1951

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Alex, you didn't really answer his question - your comment would apply if he was getting clipping of his audio wave form, but instead Stensvaag is getting noise spikes.

But having said that, I don't know the answer. Surely it would be a standard audio editing feature to be able to put a maximum volume limit on an audio track?
 

Alex Wilson

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Hey David. Stensvaag wanted an automatic way to get rid of all of those spikes, and--since it is something that is preventable in the import process (unless it's part of the original recording), which s/he detailed--the best and fastest way to prevent them is with a more careful import. Re-importing in realtime using better line levels will likely take up less time than finding and reducing each one the way, and will result in a better final recording. I don't believe simply lowering the master track's volume level will get rid of the spikes relative to the rest of the recording.

That said, it's entirely possible that I misunderstood Stensvaag's problem. I apologize for adding further confusion if that's the case.

Alex.
 

david1951

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Alex, I'm sure YOU don't need to apologise - you know more about audio recording than I am ever likely to learn! My own interpretation might well be wrong.

Stensvaag? Any idea where the spikes are coming from?
 

Stensvaag

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david1951 said:
Alex, I'm sure YOU don't need to apologise - you know more about audio recording than I am ever likely to learn! My own interpretation might well be wrong.

Stensvaag? Any idea where the spikes are coming from?
I agree that no apologies are needed. Thanks for any and all ideas.

I haven't been able to isolate why I am getting these spikes, and it may be that I will simply have to put up with them. They seem to be less violent in the ears than I had feared, possibly because the thickness of the line representing the sound is so darn thin. :)

In any event, I've been grateful for the postings.
 

moriond

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Stensvaag,

I doing my sound editing on my Mac, but here are a few ideas. Can you normalize a sound segment and apply these values to the rest of the recording (e.g., select a section of the soundtrack without spikes, have the software find min and max values, and then make these scale to be the full range of the rest of your recording)? This should result in clipping the maxima to the values on your "clean" sample.

Alternatively, is there a way of automating the spike repair? Some software packages can locate spikes or silences for editing or track splitting; is there an option to tune the repair options (length of section to interpolate over, criteria for identifying spike) and apply this en masse?

The simplest thing is certainly to understand why you're getting the spikes. What happens when you experiment with the sampling rate of your recording (if that's an option)? I know that you're bypassing the PC, but you might be encountering something analogous to the CPU spikes that can occur with some audio recording programs. Maybe taking down the sampling rate (or turning off resampling, if that's being done) can alleviate the problem?

My only other thoughts are that you might look for a freeware program that specializes in cleaning up LP recordings (where noise spikes rather than "hiss" is the problem) or one which supports automating actions. Perhaps other forum users can weigh in here.

My suggestions are based on Amadeus II for Macs, which has a Repair Centre option under Sound Repair that allows you to tune the algorithm for repairing "cracks" (including using a definition that "clipped segments=cracks") and an option to apply this automatically over a selected region (which can include the whole piece), preview it, and "undo" if you don't want to accept it. You can also "normalize" recordings, which is not a bad way of recovering if your original volume settings were slightly off. Here's an example of how this setting works for Amadeus II. Maybe there's something analogous in PolderbitS? I agree that Audacity seems to have more limited editing and repair options.

Hope this helps.

Edited to add link showing normalization option for Amadeus II (from an old version of this program -- suggested as a way to clip spikes for the current discussion).
 
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