The PA900 harmonizer is not quite as good as the one in the 3x. It's the same one that the PA800 had, which was pretty darn good. Whenever I use my VoiceLive Touch2 and go back to the 900 ... I miss the extra fidelity and range, but after a while the difference fades. If you're not doing a side by side comparison ... the 900 is very good. If time or space is an issue - the internal unit is a great addition to any setup. My VLT2 sits at home for studio projects, or a serious guitar single that pops up once in a while.
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Every instrument, every voice, every sound in nature ... these are are all my private tutors ... 24/7 for free, and all I have to do is listen.