Restoration of bad audio

[Postman]

Discussion begun in another thread, restarted here to keep the other thread on topic.

Originally Posted by Postman

I want to try it on a very difficult task, to reverse audio destruction from improperly applied Dolby noise reduction. The docs I mix often use video footage shot in the '80s and '90s. Very often the audio sounds like it was passed through some type of Dolby decoder which was either badly misaligned or the source tape was not Dolby-encoded. In either case, the result is frequency-dependent downward expansion that removes all the hiss and most everything else between loud sounds and syllables of speech, with sibilances greatly exaggerated. If iZotope can tackle that problem gracefully, I'll buy it! I had a set of System 6000 presets for different types of Dolby decoders that helped, using mutiband expansion, but the results were never perfect and sometimes only marginal.

Originally Posted by garnoil

Have you tried Zynaptic's software to clean/fix your badly processed doc sound? They make a plugin to restore over or poorly processed sound (I think it is called un-chirp) and they claim it can fix a lot of poorly processed sound. I use Unveil as a focusing plugin and I find it can do amazing things *as long as it is not over-done* so may be their other plugins like un-chirp are just as good?

UnVeil which can do amazing things in certain circumstances. It saved a narration recording entirely captured from the back side of a cardiod microphone in a non-pro room! I've demo'd surprisingly good results with UnChirp too. Have not listened to UnFilter.

I hadn't considered UnFilter for repair of improper Dolby NR decode. That's an idea! UnChirp has some high freq synthesis or something that might help, I don't know. Adaptive ("dynamic") EQ is definitely required.

Dolby C noise reduction was built into a lot of ENG videotape recorders (intended for news gathering), but there were just as many that did not have it. Lots and lots of tapes were recorded without Dolby C encoding and then later dubbed on decks that had decoding. In those days no one bothered to listen during the dub, in noisy machine rooms. The original camera tapes were eventually re-used or thrown out, and we are left with bad audio.

Dolby C is particularly aggressive. There are two stages of upper-frequency companding in series with each other. They are dependent on each other. The smallest imperfection of playback alignment is magified. When the source is not encoded, the result is a life-less muffled sound quality with unnatural dynamics and highly sibilant speech. I mixed a several hour documentary about former US president Bill Clinton. Most of the show's archive materials suffered from this. I was unable to find standalone encoders (to reverse the process) so I developed System 6000 multi-expansion presets based on the Dolby B and Dolby C operating parameters. They worked, sort of, and with a lot of adjustment the results were reasonably good. It took extra days, one clip at a time.

I still run into this problem regularly and get by with EQ automation, clip gain, dee-essing. I'd love to find a better solution. Those presets were lost after a System 6000 MkII board failure (the backup was made from a MkI and was not compatible with MkII, we discovered!). Because they didn't work very well I have not bothered to rebuild them.

[FlorianE]

Hi there!

Unfilter would be my first call. It has done miracles with several badly muffled music recordings I've had to mix.
Another possibility could be DSM from here.
A few years ago some people in Hamburg wrote a compander testbed called "CompExSimPlus". Looks close enough, unfortunately on PC, but maybe worth looking into. It is not public software, but maybe they'll let you have a copy.

Or finally, after dropping electronics, could you be tempted to do some patching in Max?

Cheers
Florian

[FlorianE]

Or maybe get one of these, use in rec mode and play your files through them.

Cheers
Florian

[Postman]

Heh heh,

Hi Florian! It didn't occur to me to look for raw chips and build my own IO. I did call every local rental house and looked through eBay for a used encode/decode unit.

It's not like this problem is a new one. For many years I kept a couple channels of Dolby A/SR that could be used for encode or decode as needed. They don't work very well on Dolby C signals, though. I doubt a real encoder would work perfectly well either, since input level and channel linearity (sum of record+playback alignments) weigh so heavily on the result.

Anyway, UnFilter does sound like a valuable tool for this and other things. RX Final Mix could have what it takes too.

[Chief Technician]

Originally Posted by Postman

Dolby C signals

(Dolby B) + (Dolby B) = Dolby C

Do you have two Dolby B units? Cascade the output of one into the other and that second output might be usable.

[Postman]

Dolby C is similar but not the same as to two B types hooked together in series. Different frequency rotation points, different thresholds for each half of the C process. With enough gumption one could buy a cassette deck that has Dolby C from eBay and modify it for line in/out. It would take a little work, probably would have to disable parts of the record amp and bias oscillator, but might be interesting.

What I discovered with my earlier Sys6k presets (which were modeled as closely as I could to the technical parameters of Dolby C), a lot of fiddling with thresholds helped recover a more natural sounding result. I have a feeling you'd want to do that even with real Dolby C decoding, to make up for all the unknown processing and copy errors introduced into the source over the years.

[Serge Perron]

There was a standalone Dolby C unit made by Dolby, but I don't recall the model number. I used it on one project at least 10 years ago to properly decode audio that probably originated on betaSP. No other decoder sounded right on this source. That was a different situation from yours, but I think the unit encoded as well. It looked similar to a Dolby 360. It was pulled from the attic of a facility for that project and may never have been used since.

That unit would be difficult to locate now if it hasn't been sold or discarded, but if you're stuck, please PM me and we'll pursue it from there.

Serge

[Postman]

That is a kind offer, Serge. I might jump at it IF the unit is easy to locate otherwise probably not worth the time. We have other options, and hopefully they can be plugins! Dragging out hardware for this does not feel as "fun" as it used to!

[minister]

Florian beat me to the suggestions. I would try Unfilter and Paul Frindles DSM. I don't use either of those very often, but on certain things they are magic. It's just rare I need them.

In the days of old, the BBE Sonic Maximizer (balanced 442 model) worked, and then I got the SPL Tube Vytalizer. Like the BBE, only better. They had a way of "tightening" the high end. The DSM KINDA does the same thing.

[FlorianE]

Hi!

Just curious: how did you solve it in the end?

Cheers
Florian