Switch the current synth to synth_name but only for the duration of the do/end block. After the do/end block has completed, the previous synth is restored.
Introduced in v2.0
Example
# Example 1
play 50
sleep 2
use_synth :supersaw
play 50
sleep 2
with_synth :saw_beep do
play 50
end
sleep 2
play 50
# Plays with default synth
# Plays with supersaw synth
# Plays with saw_beep synth
# Previous synth is restored
# Plays with supersaw synth