Determining audio cassette noise reduction encoding type?

[jbd5010]

I have a large number of cassette tapes I'm going to capture to digital. These tapes were produced church organization back in the late 70's/eary 80's, so they are not commercially available material. Despite being professionally produced, they are not labeled as to what type of noise reduction encoding they contain (if any). It is possible that noise reduction encoding was not applied since they are speech, not music.

Is there a method (automatic or manual) way to determine if a noise reduction encoding is present and, if so, which type was used? Is there a way to tell from looking at a spectrum plot perhaps, if automatic analysis software is not available?

I realize the main point in this case would just to keep the speech intelligible and minimize noise, and that frequency and dynamic range are not as critical in speech as in music recordings, but I anticipate I will be working with music cassettes soon so getting input on this is still important to me.

[Cornucopia]

Choices available to cassettes:

1. NONE
2. Dolby-B
3. Dolby-C
4. DBX

Dolby type C was not in common usage except in the BEST cassette decks, and those were $$$ and only in the mid-later '80s.
DBX is rare for any type of non-studio media, especially cassettes.

So, it's either Dolby B or none.

There isn't really any way to "automatically" determine if Dolby B was used or not. You might be able to do some long-term statistical work on the samples and finally arrive at the conclusion that there was some compansion used in the treble, but it's not worth the effort.

NR of this type does not prioritize music over speech, so there's no accounting for that one way or the other. The best way to come to some conclusion is to look over their records at the time and find out what decks they had purchased and then look up those models' manuals to see if they utilized Dolby B or not. If they did but with a manual engage, you still don't really know...

I suggest you capture as-is, without NR. Dolby B expansion can be applied as a digital filter AFTER THE FACT of digitizing, so you can digitize and then play with A/B'ing off versus on to find out which sounds best.

Remember, AT MOST, with Dolby B you would only be getting ~10dB of NR (and that only in the treble range). You can probably do more digitally with many of the common NR filtering techniques and plugins available to most Audio Editor/DAW apps.

Scott

[aedipuss]

dbx wasn't quite that rare. it was used in JVC cassette decks for quite a while. they used their own "version" with some other name i can't recall now, but i remember using it through most of the 80's/90's.

[jbd5010]

Thanks for the info. I'm 24, so I wasn't around when this technology was actually being produced and used... trying to play catch-up! Just picked up a decent Nakamichi deck off of eBay... the MR-2. I realize the Dragon is the holy grail of decks, and others like the Tascam 122MKIII, but I got an MR-2 because it was easier on my wallet at $80 shipped

Now I just need to play with Audacity and see how much improvement I can get with that. They made a significant update to their noise reduction with version 1.3.13 that I have yet to try out. Again, if money were no issue I would just get iZotope RX 2 Advanced!

[turk690]

I occasionally capture audio off cassettes. But with the majority of these 20-30 years old, it's hard to tell exactly whether or not noise reduction was used, and what type. And coming from a wide variety of sources where the tape heads may or may not have been optimally aligned, I find it's more worth doing with the cassette door permanently opened and a non-metallic screw driver to tweak the head alignment to oh-so-subtly just bring out the high frequencies. The random quality of the tapes I capture has also made it difficult at times to distinguish if there are improvements using a 3hd deck over a 2hd (I use ancient Pioneer CT229 and Kenwood KT1060). I capture with Adobe Audition, and IMHO, it's this program's noise reduction feature which brings about the sought-for noticeable changes most of the time, used in the right manner, in cleaning up the captured audio compared with switching the deck's NR switch between off, B, & C.

[aedipuss]

the few tapes i convert these days are usually on much poorer quality tape than was available back then and tape noise is a problem no matter what nr was used.

if i don't know if or what nr was used i try them all and pick what my ears feel is best, then work with various plugins.