LEDs in the audio path - linearity?
Since you're refusing to provide the circuit in question, this can only be a generic answer.

When diodes are used for signal switching, there are two considerations with regard to the magnitude of the signal relative to the DC control signal.


In the blocking state, the reverse bias voltage must be greater than the peak signal voltage in order to prevent signal leakage. Also, a high bias voltage reduces the parasitic capacitance through the diode.
In the on state, the forward DC control current through diode must be greater than the peak AC signal current, and it must be enough larger so that the current doesn't approach the "knee" of the diode curve too closely, introducing distortion.


In the latter case, a large value of VF for the diode reduces the signal margin relative to the control signal.