porta studio speed issue

O

opaz

New member
Hi

I want to digitise some old 4 tracks cassettes I made with a high-speed porta studio years ago. I've noticed that a lot of the porta studios for sale on eBay are actually normal speed. So I am wondering if I can simply play my high-speed cassettes through a normal speed four track and then slow the resulting track down to normal speed using computer software?

Thanks in advance

opaz
 
Theoretically, that is possible, yes. In practice, it might cause tracking errors on the noise reduction. You'd need to speed the recording up, not down, by the way.
 
Sorry yes - speed them up!

"tracking errors on the noise reduction"

Can you say any more about this?
 
Were those high-speed cassette decks running at twice the normal speed...or some other high speed?

'Cuz how much you increase the sample rate (or how ever you do it) after digitally recording, would depend on knowing that high-speed/normal speed ratio.
 
opaz said:
Sorry yes - speed them up!

"tracking errors on the noise reduction"

Can you say any more about this?
Click to expand...

The DBX noise reduction used by Tascam Portastudios as an alternative to Dolby (some other brands of home multitracker used actual Dolby), could be corrupted by extreme low frequencies present in the live sound. These ‘subsonic’ frequencies could not be recorded, and were therefore absent from the playback, disrupting the DBX’s ‘mirror image’-dependent process of compression and expansion. For some models of Tascam four-track, users subject to problems with ‘sub’ frequencies were advised by the manufacturer to place a high-pass filter at the record input and electronically filter out extreme lows before the DBX picked them up.

See : Ten Things You Probably Didn’t Know About Portastudio Recording | Tape Tardis
 
opaz said:
Sorry yes - speed them up!
"tracking errors on the noise reduction"
Can you say any more about this?
Click to expand...

If you used noise reduction on the recordings, e.g. DBX or Dolby, they are built on the assumption that what you're playing is the same as what was recorded. If you play it back at half-speed, the DBX or Dolby decoder is going to get a vastly different frequency ranges than were intended for the recorded piece. This may cause the volume to jump or act erratically. I've never tried doing this and don't really have the equipment to try it so it might not be noticeable.
 
OK, thanks all.

Mebs I'll try and get a double speed playback machine then.

If memory serves, the quality of the recordings at the time wasn't that great to start with.
 
Can vs. Would

Yes, you can do that.

No, I would not recommend that approach.

Why? It's just too fidgety with software methods & potential for introducing anomalies. There are frequency shifts and so on that get introduced when you play back a tape at other than it's "normal" speed. I think getting a high speed Porta for playback is a better solution, in general. YMMV.
 
As others have said, yes, it can be done but switch the noise reduction off and, if it is dBx, do the noise reduction in software after changing the speed. If your machine used Dolby B then U-he's Satin will decode it but I don't currently know of any software decoders for Dolby C or Dolby S. On other thing to watch is that your low frequencies may also be curtailed when using this method as coupling capacitors and head design will set the low frequency limit.
 
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