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I think you should use transistors with greatest possible Vth in order to achieve better linearity when signal level is high.
Schematic ??
A simple voltage divider - one resistor and one transistor.Even DC bias is unnecessary.
What worries me is the relationship between gate voltage and attenuation.
I don't know if it will be the desirable one.
FET's like BF245 can be used as audio attenuator for signals up to 1Vpp. Distortion can be about 20%. FET is not linear resistor at Vds=0. Linearity for Vds<0 decreases as Vgs approaches 0V.
The linearity of the JFET can be greatly increased by using a form of feedback. One resistor from the drain to the gate and another from the gate to the external world. Apply the control voltage to the far end of this second resistor. Use the drain and source terminals like a resistor.
Siliconix makes special JFETs designed for variable resistor service. **broken link removed**
They also have application notes for using them. https://www.vishay.com/docs/70598/70598.pdf
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