Subject:Restoring Old Tapes

Posted by: Musition

Date:8/12/2009 4:14:33 PM

Hello, I was wondering if anyone had any general advice on restoring old cassette tapes.
A bit of background on myself: I'm an amateur, hobbyist musician. I've never worked as a professional sound engineer, but I have decent math skills. So explaining things as having trigonometric or logarithmic relationships is fine (or in terms of derivatives and integrals... my differential equations are a little rusty though).

So far I've been using a combination of compression, EQ, and noise reduction. I'm completely wingin' this. I have no friends or acquaintances that are in this field. If this is completely backwards I'm not aware of it, but I've had somewhat good results. I usually start off with noise reduction, then EQ and compression. Then I normalize everything, but of course that brings the noise floor up again, so I wonder if I should save it for last. Also, some things throw me off, like, one time I was trying to restore a tape of a high school friend of mine (that he made in high school). I felt some definite compression was needed, but when I applied it, it sounded a little distorted. It wasn't much at all - like 2.2:1, so I kept experimenting, and I kept hearing distortion until I got down to about 1.3:1 or 1.2:1. Is this normal? I have no real frame of reference on these things and would love to hear some professional advice.

Subject:RE: Restoring Old Tapes

Reply by: Chienworks

Date:8/12/2009 5:33:21 PM

Noise reduction should always be done first. It works by identifying a constant noise "print" and removing this. If you do any other processing then the tape noise is no longer constant and noise reduction won't be able to remove it properly.

EQ can easily push the signal above 0dB which will introduce distortion. Use the preview function and watch the meters closely as you adjust the EQ. If the levels get too high you can reduce the gain control right in the EQ screen to compensate. You can't get rid of distortion by turning the volume down after the fact, so you have to make sure it doesn't get introduced to begin with.

There should be no need to normalize and compress separately. All the compression features have the ability to adjust the gain while compressing so it's best to do these steps together. Generally less compression is better, but the threshold matters as much as the ratio. If you have just a few loud peaks you want to tone down then a high threshold and very steep ratio work well.

In generally less processing is better. Every time you do anything you introduce errors, so fewer steps is better.

Subject:RE: Restoring Old Tapes

Reply by: jumbuk

Date:8/12/2009 11:12:20 PM

One BIG issue I have always had with cassette tapes is the noise reduction system used to make the original recording.

Most old cassette systems had the options for Dolby I, Dolby II or none. In my experience, most people who had casette players had no idea what system was used to make the recording they were playing back. In many cases, even commercially produced tapes were not clear - they might just say "Dolby NR" without indicating type. Many times, I heard people playing back a tape that was clearly recorded with Dolby, but they had NR switched off, and you could hear the pumping.

There is also the issue of tape type. Personally, I always used CrO2 tapes, no longer than 45 minutes. I used Ferro tapes for mastering my own stuff.

So, my point is - problems with compression, NR and pumping can sometimes be traced back to differences between the recording and playback settings. You need to get these right before making your master digital recording from the original tape.

My restoration chain is as follows:

- Sony NR using a noiseprint from the tape leader

- Waves C1 expander to eliminate any residual noise

- Waves EQ to tidy up the balance

- Maybe a mild amount of a Waves Trueverb patch if the original was lacking in ambience

- Waves L3 to dither and maybe add a bit of perceived sound level

Distortion in compression could be caused by attack or release settings, or maybe just the input gain being too high.

Subject:RE: Restoring Old Tapes

Reply by: musicvid10

Date:8/13/2009 11:15:10 AM

There is no need to add compression or limiting when recording from cassette tapes.
It is already a low-headroom format, and compression will raise the noise floor from any point above the threshold, which only makes noise reduction more difficult.