Almost every trombone method that teaches legato explains that legato is one of the most difficult to master techniques on the trombone. The statement is often made: “A young trombone student must spend sufficient time to perfect this technique.” This means that no one learns legato in a week or a month. It is ok if things don’t go smoothly at first. It will take time – probably many years to start feeling confidence in all aspects of legato playing.
The first and most important thing when learning legato is to know how you want your legato to sound. This is an opinion. Not all trombonists agree on what legato should or should not sound like, so if you have an idea of how you want your legato sound to be – so be it. Listen to lots of recordings of great players playing legato. Listen to classical soloists, and jazz soloists. Listen to players on string, woodwind, and other brass instruments. Keep in mind the trombone probably can’t sound exactly like other instruments because it is not like any other.
Next, I would recommend a private teacher. If nothing else, you need to have another set of ears to hear what you are doing. Recording yourself is another great way to hear what is really coming out the end of the bell. There are programs on the internet that can slow the playback speed down and you can really tell if the sound is legato or not. Tape recorders with half speed switches are also great tools.
It is fine to make glissandos in the beginning of legato development. In fact, it is better to make a glissando than a disconnection because keeping the flow of air is the most important part of legato playing. My opinion is that before the legato tongue is introduced, all slurs should be glissed (except those that can’t be). This way it is easy for you and your teacher to know if the air is constant.
When you start attempting legato tonguing, the most common syllable to use when tonguing is ‘D.’ Place an open vowel on the end and make it ‘Doh.’ This will be a good start. Remember, trombonists use the tongue to cover the glissando sound as the slide moves, but should not block the air any longer than needed. After some time experiment with different syllables such as D, L, N, or even R (a quick flip of the tongue used in Latin languages such as Italian or Spanish) to see if another syllable works better for you.
Practice legato etudes such as those in Reginald Fink’s “Studies in Legato” book or for more advanced playing the Concone Etudes transcribed by John Shoemaker or Rochut’s transcriptions of Bordogni Etudes. Do these etudes with legato tongue and without to practice constant airflow.
After many hours of practice, you will eventually get to the point of sounding the way you envisioned back in the beginning stages of legato practicing.