The best replacement for synth is keyboard.

The best alternatives to synth are rated as following:
★★★★★  keyboard
★★★  workstation
★★  midi
★★  midi controller
★★  sampler
★★  hardware
★  sampletank
★  digital piano
★  software synth
★  soft synth
★  lucina
★  hard synth
★  access virus
  analog synth
  stage piano
  vst
  hardware synth
  software
  ax 09
  real synth
  ax-09
  sound module

Your alternative for synth is not listed? Suggest!
Speaking about synth, one probably shouldn't forget about drum machine.

Other search terms related to synth and their ratings are:
★★★★★ drum machine
★ built in drum machine
You have in mind a companion for synth and it is not yet here? Propose!



Google Trends

Scale is based on the average worldwide traffic of synth in all years. Click on graph for more.
synth
keyboard
workstation