I'm not clear regarding this additional polyphony. If one arranges a performance using factory performance and adds user, then saves the new performance we now have an additional 128 poly?

No - the polyphony limits are based on 1) the engine being used and 2) where AWM2 waveforms are stored. The docs don't explain it well but the Ops doc does allude to the limits on page 584 in the troubleshooting section for the topic 'The sound is cut off'

The sound is cut off
Is the entire sound exceeding the maximum polyphony?
AWM2 (preset waveforms): 128 (both stereo and mono)
AWM2 (user or library waveforms): 128 (both stereo and mono)
FM-X: 128
AN-X: 16

The AN-X engine limit is 16

The FM-X engine limit is 128

AWM2 (preset waveforms) limit is 128

AWM2 (user or library waveforms) limit is 128

All presets use preset waveforms. If you create your own performances, or add parts to a performance and use elements whose waveform is a preset waveform the limit is still 128.

You get an ADDITIONAL 128 if you create your own user waveforms, or create/load a library that has waveforms in the library. Waveforms in a library are considered user waveforms.

That is the ONLY way to get additional AWM2 polyphony - using user waveforms or library waveforms.

Thank you for a much clearer explanation!

In a recent thread a user ask why voices were cutting off in their M so I provided a step-by-step example of how easy it can be to exceed that 128 polyphony for presets

https://yamahasynth.com/community/montage-series-synthesizers/voices-cutting-off-in-montage-m-firmware-2-0/#post-125287

Yamaha's parting gift to the Montage classic users is great because there are some good pianos you can load into M from the previous gen to build Performances that do not use preset samples (except maybe key off).  Or use the previous Imperial pianos for the same purpose.  

Of course the 3rd party content that uses custom samples becomes more attractive as a way to extend polyphony.

And if you had a Montage classic and use Sample Robot, you can sample in your M to create user versions of Performances too.  

Posted by: Jason

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And if you had a Montage classic and use Sample Robot, you can sample in your M to create user versions of Performances too.  

Yeah, that is odd that the Montage M has an extra 128 notes of polyphony for AWM2 User/Library Waveforms, as well as near double the User/Library memory, but they didn't include SampleRobot so that new owners could create their own more easily..!?

But like you said, there are free Yamaha libraries, as well as 3rd party ones that can be loaded with non-preset Waveforms, which can utilize the extra polyphony...

I also read something about SampleRobot working on a version for the Montage M, so that may be a future option...

And for now there are still free utilities you can download and use to sample/create/modify .wav files that can be imported into the Montage M, such as Audacity!

...and basic ones via Cubase or your DAW of choice 😉