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Cassette to Digital, trying to copy hundreds of cassettes to a pc
DanDaManJC
post Jul 9 2008, 00:10
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Hello all! Well my dad is trying to copy his collection of sermons and seminary lectures from cassette to pc.

Using audacity, lame, headphone out on the cassette player and the line in on the pc we are able to convert the cassettes to mp3. The sound quality's just fine for our purposes, however the one major problem is that the cassettes are being copied in real time and my dad has hundreds of 90 minute tapes collected over the years.

So basically the question is: how can we do this fast? My dad actually has a Telex Copyette 121 mono cassette duplicator, which according to him, copies tapes at 16x (else it copies a whole side in a couple minutes). But it doesn't have any kind of analog out which I could plug into a pc. One idea that came to mind was to use the cassette duplicator and then instead of copying to a blank tape, instead use one of those car cassette -> cd player adaptors... however that is "backwards" since the cd player inputs to the cassette player while in this case we want the cassette to output to the "cd player" (in our case obviously the pc). We also tried that... and it didn't work.

Furthermore, would we run into aliasing issues if we did manage to sample these cassettes with the tape duplicator my dad has? We'd be using a normal 44khz sampling rate too.

A more far fetched idea of mine was to add an output to the tape duplicator that could used as an input to the pc... iono, try and figure out where the signal is and then get the right impedances and stuff. iono how i'd do it though :-/

Well thanks for the help guys!
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DVDdoug
post Jul 9 2008, 01:32
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I'd probably just "bite the bullet", settle-in and get to work... Or, you could look for a company that will do it for a fee. They may have parallel systems, so that they can run several transfers at once. You might be able to do something similar, depending on how many computers & cassette machines you can get your hands on.

QUOTE
A more far fetched idea of mine was to add an output to the tape duplicator that could used as an input to the pc... iono, try and figure out where the signal is and then get the right impedances and stuff. iono how i'd do it though :-/
There is a good chance that will work! (But, I'm worried about the high frequencies at 16X.) If the thing has a separate circuit board for each transport, you might be able to see where the audio is connected. Or, if there is a level control, you can probably tap-off of it. Ideally, you would have a schematic and an oscilloscope to "track-down" the signals.

The input impedance on your soundcard is high-enough that it's unlikely to damage the duplicator's electronics if you hook it to the "wrong" place. But, there is always that possibility, as well as the slight possibility that you'll damage your soundcard.

QUOTE
Furthermore, would we run into aliasing issues if we did manage to sample these cassettes with the tape duplicator my dad has? We'd be using a normal 44khz sampling rate too.
No. When you speed-up the tape, you will have some supersonic frequencies that could cause aliasing, but your soundcard has (or should have) a digitally-controlled low-pass analog filter to prevent that problem. Simply recording should never cause aliasing, and if you change the pitch/speed together, that shouldn't cause aliasing either. (You can get aliasing when you downsample and preserve the pitch/speed.)

At 16X, you'll have to use a higher sample rate than 44.1kHz.... When you reduce the speed back to normal, your Nyquist rate (The highest frequency you can record/store = half the sample rate) will decrease proportionally. At 44.1kHz, you are limited to 22.050kHz. If you reduce that by a factor of 16, you are down to ~1400kHz which is going to sound terrible! With a sample rate of 192kHz, you could theoretically get audio up to ~6kHz, which might be acceptable. But, that assumes the soundcard can actually record supersonically up to the Nyquist limit at 192kHz... I'll bet most soundcards cannot do that.
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pdq
post Jul 9 2008, 05:03
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I'm afraid you're out of luck with the tape duplicator. Your best bet is multiple tape players and multiple sound cards, or multiple computers.
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DanDaManJC
post Jul 9 2008, 05:24
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Thanks for the help you guys

Looks like we'll have to make do unless I haxxor that tape duper smile.gif

Edit:

on a quick note, would I be able to obtain the schematic to the copyette? or is that all proprietary?

This post has been edited by DanDaManJC: Jul 9 2008, 05:31
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DVDdoug
post Jul 9 2008, 18:52
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Sometimes, a (reduced size) schematic will be glued to the inside of the cover/back panel. Otherwise, you might find it on the Internet, or you might find one for sale on the Net. Schematics for consumer products are copyrighted, but they are usually not proprietary because repair shops need them.

I was able to get a complete repair manual (with schematics) for my TV by searching the Net (I think it cost me about $20 USD).

But, I am concerned about recording those high frequencies... Are there any other speed options? I'm pretty sure 2X would be fine, and I suspect 16X is going to be trouble...
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Marky Mark
post Jul 9 2008, 19:26
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DanDaMan - I didn't do hundreds of tapes like you have, but I had some cassettes my grandfather had made that I wanted to capture to computer in order to preserve for family. I too toyed with the idea of playing the audio at increased playback rate for recording but the paranoia of possible data loss (or additional sound quality degradation due to high-speed playback) on already less-than-perfect data coupled with the thought of having to do it over again if I wasn't happy with the results swayed me to just plan a few weekends for capturing the audio at 1x. The good thing is you can set the timer on your microwave for 45 minutes and go do other stuff. smile.gif

You said you were content with the audio quality, but I used Goldwave and captured at 24/96 resolution to allow more headroom for post-processing (hiss/hum removal, etc.). Again, I wanted to limit how much additional quality loss occured from the already imperfect original. Like you, I then encoded the files - but to FLAC, so that I had the archive, before transcoding to mp3. I am not claiming 24/96 made it sound better, just that it gave me peace of mind to feel free to post-process without worrying too much about losing quality from the recording.

-M
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M
post Jul 9 2008, 20:56
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QUOTE (DanDaManJC @ Jul 8 2008, 19:10) *
Hello all! Well my dad is trying to copy his collection of sermons and seminary lectures from cassette to pc.

My father-in-law asked me to help with the same sort of project, and while I do have a the capacity to transfer his sermons in real-time on professional equipment, for ease-of-transfer I've been looking at one of these.

- M.
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