So for the first year or so I kept announcing the tandas vocally in our local milonga. But the habit didn't stick, especially after I started DJing bigger events. Fast forward a few years: in one of the tango marathons I saw Mikael Holber using a program he created himself to project the names of songs and the next tanda on a screen. What a super solution! Mikael, teaming up with Horia Uifaleanu, later released the software to the public. Their project is called Beam and you can download the program from their website: beam-project.com. To be honest I haven't tried the program myself, but from what I've seen live and from what I read it is already very useful and keeps getting better!
Recently I also started another project which culminated in a similar result. I have a pretty bad voice, but I love singing along tangos, especially those of Carlos Gardel. So I wanted to display the lyrics of the songs while they play so that I can sing along. A number of programs are available for doing this; the larger part of the effort is in finding, correcting, and synchronizing the lyrics with the music. (Although I was vaguely aware of this before, during this work I needed to realize that most of the lyrics that is available online - for instance over one of the most awesome tango resource site, Todotango - is only partially matching the lyrics that is actually sung by the singer. There are also subtle differences between different renditions; i.e. have you ever noticed the different wording Ernesto Famá (with Francisco Canaro) and Fernando Díaz (with Francisco Lomuto) chooses when singing Parque Patricios?)
After few weeks of work I ended up having many hours of tango music with synchronized lyrics. Although I started my synching spree with Gardel, I mostly focused on well known, danceable songs that fit nicely together in tandas.
And so recently I experimented with something new: with an entire night's worth of synched tandas I used the built-in video projector in our regular milonga at Kazimir haz to display the lyrics to the dancers. Here is a video of an Edgardo Donato tanda from 1939-40 with Sinfonía de arrabal, Mi Serenata, Yo te amo, and Carnaval de mi barrio to show how the screen looked like. (Milonga footage is appended to the end!)
I was a bit worried in the beginning that displaying the lyrics would distract the dancers, but that didn't seem to happen; on the other hand those who were sitting during the tandas could hum along the lines. The response was overwhelming, and a very positive experience; I think I'll keep coming back to this after I finish processing another few hours worth of tandas.
I'm also looking forward to the summer tango camp of Endre Szeghalmi and Maria Glotz where I'm going to DJ together with Konrad Krynski (our partner in crime in organizing the regular Thursday milonga in Budapest) and Luca Csatai. After the Friday milonga, when some people are already a bit tipsy (if past traditions are properly followed!) I'm planning to create a huge tango karaoke party! In general I think karaoke for tango songs could work well for after-after-parties of tango festivals and marathons, when people who had enough dancing can hum along their favorite songs!