I sort of promised to post a few samples of my results from slowing down some tracks that I believe are transferred at too high speed in the DyM Tango Classics collection.
Although I have suspected that several other transfers, most notably on the El Bandoneon label were transferred at too high speed, I never tried slowing them down myself because I knew it to be hard to find the correct speed. Maybe impossible. To know you got the right signal (as in as similar or undistorted relative to how it sounded before it entered the recording chain), you would have to know the tone played at some time during the recording, and how the instrument that played that tone was tuned. Even though there are scores for many tangos, the exact arrangements are rarely available, and even then you would have to know that the musicians did not deviate from what was written there (e.g. transposing up or down a (semi)tone). And how the instrument was tuned. Most commonly the concert pitch A is supposed to be 440 Hz, but it has varied from time to time and from orchestra to orchestra.
Not trivial in other words as I basically had access to exactly none of the required information. I usually tried to get another and hopefully more correct transfer, leaving the problem to be sorted out by someone else.
Now with some of these De Caro recordings, it was just too annoying, and I didn’t know of any other transfers available (which was why I got them in the first place). So I gave it a try. As I don’t have perfect pitch and didn’t have the above mentioned information, I did it by trial and error, and I paid particular attention to the timbre of the piano, attack, decay etc and generally tried to assess whether it sounded ‘right’.
I would be interested to hear your opinion, here are two examples, both by Julio De Caro, El taita/Raza criolla and Maipo. First original as transferred by DyM, then my 7 percent slowed down versions (about one semitone). EDIT: I added some samples for tracks that I believe are not so readily available: Berretín and Lorenzo.