Legal Question in Entertainment Law in California

Copyright experts like to say that copyright is a bundle of rights, not a single right, and your question underscores that principle. In fact, you are asking about several bundles of rights.

First, live performances are not copyrightable. Copyright applies when a work is "fixed in a tangible medium of expression," so the person who fixes it (in this case, makes the recording) owns the copyright in the work (in this case, the tape recording). If you recorded the cassette tape, then you would own the copyright in the recording. On the other hand, if the recording was done by a record company or someone else, it belongs to them and you need to obtain rights.

If you made the recording as an employee of someone else, then your employer owns the copyright. For example, if you worked for the school and running the tape recorder was part of your job (or your assigned extracurricular duties), then the school owns the recording.

That does not, however, give you copyright to the music, which is owned by the composer who fixed the notes on the sheet music. Usually, the music's publisher owns or controls the rights to sheet music. If the music is in the public domain (works by long-dead composers such as Beethoven and Mozart fit in this category), then no copyright applies. If the music is copyrighted, you need to track down the copyright owner and obtain permission to use the music.

If any of the persons on the recording were identified or easily recognizable, you would face a different set of rights problems. But for an audio recording, it is unlikely those would be an issue in the scenario you describe.