did not work because of missing return - for num_channels<=1, "left channel" was still running..
(1  means pass trough)

In my testsketch with 2 x Chorus with n_chrous=4 & #define CHORUS_DELAY_LENGTH (24*AUDIO_BLOCK_SAMPLES),
Cpu-usage decreases from 13.8% to 9.8%

https://github.com/PaulStoffregen/Audio/pull/7