An urgent message about digital noise reduction

[tungarbulb]

I’m glad I found Trader’s Den. I wish I’d found it 20 years ago. (I know that would have been impossible, but what the heck ). Just the same, I need to say something for the benefit of novice sound processors and ultimately the whole trading community.

So far I have downloaded two shows from here via torrent which contain very noticeable digital artifacts as a result of overzealous de-noising. These artifacts - which sound a lot like hearing dozens of wind chimes in the distant background (any sound pros and savvy tapers will know what I’m talking about) are WAY more annoying to listen to than the original analog tape hiss.

When I was getting started with digital sound processing, I too wanted to scrub my analog originals until they sounded like born-digital recordings. I found out the hard way that you can’t do that. You end up killing the high end (something which digital de-noising was supposed to do away with) and introducing the digital janglies which I’ve described above. Listen to some very good commercial CD reissues of analog-source recordings, and you’ll find that some tracks, even ones from major bands like the Stones, have just a touch of residual hiss in the background. The engineers who make their living restoring old tapes know that trading a smidgin of analog hiss for digital distortion, diminished frequency response and other artifacts is not the thing to do. Their equipment is probably a lot more sophisticated than anything we have too. If they can’t make an old master tape sound perfectly noise-free, neither can we.

De-noising is a balancing act. The object is to find the point at which de-noising starts doing more harm than good. Think of it like planing a door to fit a particular doorway. If you very carefully shave off a little wood at a time, you’ll eventually make the door fit properly. Shave off too much wood, and the door will be too small to close properly. Plane the door too fast, and you might gouge the wood. Your digital de-noiser should be set JUST at the point where noise is reduced to a tolerable level and no artifacts have surfaced. A good sound card, amp and headphones will help you a lot. (Most “computer speakers” and built-in sound cards are not suitable for serious audio work, but you already know that.).

Keep the good stuff coming, guys. And I implore you once more, please don’t try to make an old analog recording “sound like a CD”.

[gsmyth79]

I think it's the policy of TTD to seed unmodified sources. If they are modified the seeder probably notes it...

Which seeds are you talking about specifically? Does anyone else notice these issues in the thread?

Oh, and welcome to the Traders' Den!

[Lou]

I completely agree with the above post, I'd call the sound "glassy" but it's just an awful sound. When I transfer tapes I NEVER, EVER digitally noise reduce them. I'll only very rarely do traditional noise reduction on the tape deck if I'm going to noise reduce at all. It's gotta be a really harsh noise for me to noise reduce on the deck.

[Five]

Leave denoising to engineers only, please. If ppl want to up noise-reduced shows we will still accept them with proper documentation in the lineage. Some of the noise-reduced shows I've downloaded have been like a trip thru the FLAC cancer ward. So please avoid nr or if you insist be very very very careful with it.

Great first post, tungarbulb.

[AAR.oner]

good post tungarbulb...this is something we can't stress enough...

[tungarbulb]

Originally Posted by Lou

...When I transfer tapes I NEVER, EVER digitally noise reduce them. I'll only very rarely do traditional noise reduction on the tape deck if I'm going to noise reduce at all. It's gotta be a really harsh noise for me to noise reduce on the deck.

I'm a DJ and sometime sound engineer, and I'm pretty much a minimalist. I agree with you that processing should only be done if necessary and only if it makes a noticeable improvement. I'll usually run the de-noiser if the noise on the tape I'm working with is really objectionable. One of my first de-noising projects was a telephone interview which was made on cheap equipment and which also had phone system noise all through it. It definitely took a lot of trial and error (on a 233 Mhz AMD K6!) before I found out how to get rid of the noise without creating new problems, but what a relief to hear the voices minus the garbage!

[tungarbulb]

Originally Posted by Five

...Some of the noise-reduced shows I've downloaded have been like a trip thru the FLAC cancer ward.

Very good analogy. There's nothing like spending hours downloading a promising set only to find that it's been digitally mutilated.

First-time de-noisers should definitely spend a good amount of time practicing up on unimportant recordings or expendable duplicate copies of important ones, until they get good enough to use NR without wreaking sonic havoc.

BTW, thank you all for your kudos!

[guygee]

Originally Posted by tungarbulb

(...)
De-noising is a balancing act. The object is to find the point at which de-noising starts doing more harm than good. Think of it like planing a door to fit a particular doorway. If you very carefully shave off a little wood at a time, you’ll eventually make the door fit properly. Shave off too much wood, and the door will be too small to close properly. Plane the door too fast, and you might gouge the wood. Your digital de-noiser should be set JUST at the point where noise is reduced to a tolerable level and no artifacts have surfaced. A good sound card, amp and headphones will help you a lot. (Most “computer speakers” and built-in sound cards are not suitable for serious audio work, but you already know that.).

Keep the good stuff coming, guys. And I implore you once more, please don’t try to make an old analog recording “sound like a CD”.

Very well said, tungarbulb. It should be noted that booters can be just as bad as us "amateurs": I have a "silver" of a Byrds show that was denoised so heavily it sounds like they are playing underwater! Just completely unlistenable.

I once had somebody send me a tape of a show (Wavy Gravy's 50th Birthday) with a request for me to digitize it. The tape was very high-gen, the hiss made it almost unbearable to listen to, so the first step is to try and locate a better source. Unfortunately in this case it turned out that the show was barely circulated, and the best I could do was to trade for two other tapes, which turned out to be just as bad or worse. I had a decent set-up (Naks, good A/Ds, choice of Samplitude, Cool Edit or Sourceforge), but since Side A was a loud Jorma set followed by an acoustic Garcia and Kahn set, it was a real balancing act. My patron was very happy with the results, but I was upset with with slight "wavery" degradation in Jerry's delicate fingerpicking caused by the denoising. I've never circulated this show because of this, as I am torn as whether to release it in all of it's hissy glory, or to release the denoised version (which I agonized over for about 100 hours), or to wait for (or write myself) some kind of new type of denoising software that does a better job of preserving the underlying music.

[chazuke]

Regardless of what's been said against noise reduction, can you recommend a free NR software and state an URL? I have some recordings here with severe digital damage which cannot be listened unless remastered. It's more for home use and not necessarily for upload.

My opinion, btw: Some stuff must be de-noised, some can, some should not and some must not. So it depends.

[guygee]

Chazuke - I really do not know of any decent free tools out there, but you might try the "Goldwave" wave editor. It is shareware, but you can downloaded a limited demo (3000 commands total, 150 commands/session). The new version looks like it has various filtering tools:

http://www.goldwave.com/release.php

Remember that broadband noise is much harder to remove (without damaging the music) than other types of noise. For example, "digipops" are usually of short duration and can often be penciled out without leaving an artifact. Same for a single scratch in an otherwise pristine vinyl rip. Analog single-channel droputs often leave a very noticeable noise, even when the dropout duration is between 10-100 ms., but if you carefully cut to mono (try to match levels and slopes at the cut) the human ear "integrates" right though the brief mono and does not detect it.

Severe line noise can be removed by carefully constructing narrow filters at 60 Hz. and its harmonics (120 Hz, 240 Hz...possibly higher). It helps to have a frequency domain sample of the noise without any music to determine the filter parameters, and inevitably you are removing some musical content, so be cautious.

Broadband noise is the real challenge. Tape hiss, wind in the mics, vinyl crackle and rumble, and the guy with whooping cough sitting next to the taper are all examples. Hiss removal tools usually use dynamic filters that set a amplitude trigger based on a noise floor, and use attack and decay settings to try and filter from the top frequencies down, using less filtering when the music is "on" and more in the quiet spots. If way overused, you will hear this strange background, like crazy windchimes, in this case back way off on your settings.
In my experience, acoustic music is the most difficult to remove hiss from, you get an oscillation in the decay of the guitar notes ("waveriness"?) that is not unlike a bad MP3.

In any event, use your ears to compare "before and after", and see if you can find a good spectrograph tool to compare before and after to make sure you are not taking too much off of the high end and/or leaving any other "blocky" artifacts.

(EAC has a spectrograph tool, but watch out for its artifacts (false content from aliasing) in the high end, also there is Sound Software Spectrograph 1.0, not particularly versatile but at least it is free. Still available at:
http://www.sonicspot.com/soundsoftwa...ctrograph.html
)

The SF2 Soundforge Noise Reduction plug-in (direct x) is much better than others. I personally have a low tolerance for analog hiss. There are DL's I did-and deleted because they were beyond the range of what I can stand,beyond what I can fix. I built a set of very revealing speakers-meaning I hear the good stuff-and the flaws,so I want to enjoy the good stuff without a lot of crud.

Someone mentioned NR on the TAPE DECK???? Okay,a recording CAN be RECORDED in DOLBY B or C or no Dolby. To playback-you playback in the format in which it was ENCODED. You can not just push the Dolby C button on a deck and improve a recording that never had Dolby. Also-Dolby is more of a NOISE PREVENTION. it can not take away noise on the source,it does reduce the accumulation of hiss inherent in making another generation. A lot of analog tapers don't get what dolby is.

The IDEAL is to have an end result as close to how the original event sounded as possible. When the source material involves a multi-gen 30yr old analog originally done on second rate gear,it is pretty easy to improve it using GOOD NR techniques and probably some EQ. I really have no appreciation for the Audio-Vegan mindset that insists every flaw,mistake and shortcoming of the recording process has to be preserved-and yet some folks do butcher the job. The "damaged" recordings referred to above....who has the pre-processed version? Are you SURE it got NR effects and what you heard is not the effects of a badly recorded original,a bad transfer to digital? or just age?
Some recordings I have DO have some NR artifacts or other processing flaws-but were salvage jobs of a recording that was unuseable wreckage otherwise-would have joined a little stack of discs I burned before I realized how awful the sound was.

[guygee]

Originally Posted by rerem

The SF2 Soundforge Noise Reduction plug-in (direct x) is much better than others. I personally have a low tolerance for analog hiss. There are DL's I did-and deleted because they were beyond the range of what I can stand,beyond what I can fix. I built a set of very revealing speakers-meaning I hear the good stuff-and the flaws,so I want to enjoy the good stuff without a lot of crud.

I agree, I also have a low tolerence for tape hiss, and although I didn't build my own speakers, the Pro Studio speakers in my system bring out the details over the spectrum pretty well. As the owner of many "medium-gen" cassettes, I would agree that some NR with the proper tools should not be objectionable, especially if better source material is not available. Also (personally) I want to hear the singing well enough to understand the lyrics, I want to hear the bass guitar, I want to hear the top hats, and if the mix is bad, some judicious dynamic EQ'ing can bring these aspects of the music more out to the front. I am also interested in harmonic enhancers, these tools can really bring the music back from the dead, especially if the original recording is overly band-limited

Originally Posted by rerem

I really have no appreciation for the Audio-Vegan mindset that insists every flaw,mistake and shortcoming of the recording process has to be preserved-and yet some folks do butcher the job. The "damaged" recordings referred to above....who has the pre-processed version? Are you SURE it got NR effects and what you heard is not the effects of a badly recorded original,a bad transfer to digital? or just age?
Some recordings I have DO have some NR artifacts or other processing flaws-but were salvage jobs of a recording that was unuseable wreckage otherwise-would have joined a little stack of discs I burned before I realized how awful the sound was.

You make some good points: if the tape is really high-gen, old or partially demagnetized, the music is badly damaged to begin with. But I think part of the question is, what do we want to preserve for historical purposes? So I can also appreciate the view of the "Audio-Vegan mindset" . The technology of audio restoration will advance. 2nd generation wavelet filtering, dynamic neural network filtering based on particular artists voice prints and "instrument prints" (and high on my list, the "YeeHaw Cowboy Yell Remover Tool")...who knows what the future will bring? In that case, we want to have a copy of the original analog recording with the highest bit resolution and sampling rate preserved, in its purest "granola" form, without any previous signal processing applied. So for our present listening pleasure, remaster (if you prefer), and do it well (including careful documentation), but also archive those 192k/24b A/D files in their raw form for future generations.

[ssamadhi97]

The big problem with digital NR is simply amateurs who warezed SoundForge or Audition and believe that by doing so they suddenly became audio engineers and can magically remove all the noise from recordings without damaging them badly. Not so. In inexperienced hands digital NR can do a lot (and by that I mean A LOT) of damage to a recording, to the degree where it becomes intolerable to the experienced listener - even though the person who performs the NR might not even notice it due to a lack of experience with NR.

I guess that's what most of us are afraid of.

[guygee]

I am not sure what the difference is between "amateurs who warezed" and amateurs who buy, but if the term amateur simply means inexperienced, then what better way to train your ears than to buy or otherwise obtain one of these software packages, and try for yourself the different settings and listen to the results. I think it is great if as many people as possible have access to these tools, they will make mistakes, but over time their ears will become trained to hear the artifacts they produce, and we all will benefit. I know that is how it happened with me, going all the way back (don't laugh) to the day I downloaded "wavclean", cranked up the settings, and heard all the weird sounds pouring forth. From the experience of trying different NR and other sound editing tools, now I can easily hear the artifacts in other recordings, including on many of the overly-revered "Silver CDs" that get passed around.

I can also hear them in some of my own struggles to remaster high-gen analog sources, but when I compare to the raw source, it was just a matter of, shall we say, "Polishing the coprolite".

Now when it comes to inexperienced people actually seeding their nifty new "remasters", 1) If the original version is already circulating, who cares? Take a chance on downloading or not. Reputations are built on the quality of the seeds, and bad versions will end up in that proverbial dustbin, 2) If the seeder A/D'ed from an analog source, or from a rare/uncirculating digital source, and applied NR processing, then I think it would be fair if the seeder would offer, upon request, to distribute the raw source in the original form (hopefully 24 bit/high sampling rate) to any person claiming the experience to do a better job, or to anyone offering to archive the files on a publicly accessible site.

Actually-a big peeve of mine is torrents put out with major clipping. Some of these were recent vintage,from DAT so analog hiss is no factor,but somewhere along the line the waves got major clipping. A few clips are fixable-but if the whole thing is maxed-there's no hope. I actually have run into that more than a botched NR job. Almost as annoying-but at least fixable are those where the whole show needs a 300% volume boost-and I've DL'd plenty of those. The way I try to do it-up what is first rate. If something seems scarce-yet what I have really is flawed...odds are a better version exists,and often it appears on a bt site. Later-after I do the next puter,with a better soundcard-I'll hunt through my analogs and see what still has not appeared online. Already several have shown up-and in better quality. A few probably won't appear until I digitize them.

A note-it is VERY important that if you try to remaster/clean up audio files you have GOOD speakers...not "computer " speakers,but a real stereo amp and some quality,accurate,monitors.