Tango Audio Restoration

Tango music was recorded with equipment much inferior to what is available today. Adding to that, the record companies threw away the master’s leaving us with reproductions based on the shellac records that further deteriate the sound.

For many of the commercial releases of tango music, the Reliquias series, the 78RPM series etc, the transfers have been cleaned and the noises removed for the music to become more clear and easy to listen to. And believe me, if you haven’t listened to a shellac record from the 1920s, you probably have no idea how much noise and hiss there can be on those.

The problem is, in some cases the audio engineer cleaning the sound gets too excited about his capabilities and applies too much filtering, effectively throwing out some of the music along with the noises he is trying to remove. Because once the signal (the music) is mixed with the noise, there is no way to reliably separate the two completely again.

The industry state of the art has been the Cedar noise removal systems, which are very expensive, professional equipment. Enter the revolution of digital sound and digital signal processing (DSP).  Now the same tasks can be performed with much cheaper equipment, often with better results. Adobe Audition is an example of a product that gives you a lot of possibilities in this area, much cheaper, but still rather pricey for an amateur that wants to clean up some old tango recordings.

You see, the great thing about the CTA series of Mr. Akihito Baba is that they are close to raw transfers from the shellac records.

**P & M: **You can clean some noises during the process of recording CDs these days. **Baba: **Yes , but on the other hand I don't want to cut the noise when I reproduce SPs. I like to reproduce SPs without cutting down hig waves to reduce the noises. You can use an equaliser to cut the noises down well, but I decided not to do so. There are others who make clean sound reproductions in Japan. But there are good SP´s not containing any so-called noises, so you don't have to cut any noises. When you cut the noises, quite often it loses the other sounds as well at the same time. That's a shame as well. > > From [interview with Mr. Akihito Baba](http://pythia.uoregon.edu/~llynch/Tango-L/2001/msg00791.html) > >

The great thing about that is that you can take the old records of Mr. Baba and apply today’s computer tools that use sophisticated algorithms to clean up the sound, often with very impressive results. I wanted to check the capabilities of the free software tools Audacity and Gnome Wave Cleaner. While researching them, I saw references in various forums to a shareware software called Click Repair. It can be tried for free for 21 days, and the results are quite encouraging, even with the default settings, both for Click Repair, and DeNoise by the same author. That they produce good results with little manual intervention is important, as manual audio restoration is a very time consuming process.

I prefer a little noise to over processed sound, but I also prefer no noise to the noise of the old 78 rpms. In the continuum between these extremes, I think the sweet spot for me is more like 80%-90% clean, limiting the probability of audible distortion to the signal of interest, i.e. the music. And I have hope it can be achieved by batch processing the cta discs and others.

The thing I like almost more than the impressive results, is that the software lends itself to automation. There are some adjustments that would ideally be made for each track, and I will make those for each cd instead, and reprocess single files if they turn out problematic. From my experiments so far, the noise profiles of records seem fairly similar, and the amount of noise more or less the same on records from the same years.

To check that you are not removing any important information, you can easily switch between three listening modes, the input signal (unprocessed music), the output signal (the processed music) and the difference (the noise that is removed). By checking the noise, you can be fairly sure you’re not removing any actual musical content by applying too aggressive processing.

It is possible to get better results by doing it manually, but I have no time for  redrawing waveforms manually on hundreds or thousands of tracks. Well, not until when I retire ;-)

Here are a few samples:

This first one is a nice orchestra with recordings from the 1940s with clicks and pops that were annoying me. The software doesn’t output the noise, but I made a simulation (taking the difference between the original and the processed) to give you an idea of how it sounds:

Manuel Buzon - Al verla pasar - original

Manuel Buzon - Al verla pasar - processed

Manuel Buzon - Al verla pasar - noise

Then some material from the 1920s:

Juan Maglio(Pacho) - Alma tanguera - original

Juan Maglio(Pacho) - Alma tanguera - processed

And a nice D’Arienzo from the 1930s:

Juan D’Arienzo - La bruja - original

Juan D’Arienzo - La bruja - processed

All these are (to my knowledge) unavailable in pre cleaned versions, so a little restoration will be worthwhile. The next question is: Can the results be even better than some of the commercially processed releases? We’ll get back to that in an upcoming post.

Some readers reported difficulties with playing the mp3 files from the web player, you can download all the samples in one zip file .

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