Is your circuit that one?
What's going wrong with your circuit, it isn't behaving as expected?
That's an strange circuit, first time I see someone trying to use it. Common base, that's fine, but the other way around, using the emitter as input and collector as output.
Maybe add a previous stage as buffer, like an emitter follower or an opamp and then run this same thing at a higher current, maybe a lower hFE transistor, like a small power one, BD139 comes to mind. That way you can keep your ~100k input impedance, but use smaller resistances all around, like 10k instead of 100k and 100k instead of 2M2.
In any case, the output of that circuit will change a lot with temperature and from device from device, as NiHaoMike said.
The next option is a redesign of the thing to get a similar response, knowing the sources impedances is critical for that. The roll off is what itches to get a different circuit to do this, which seems quite important for an envelop generator.
Few options that might work, try with a lower hfe transistor with the circuit as it is, and lower the base resistor. Try scaling down both resistors, maybe not exactly together, again, this will depend on the device.
JS