Default downwards hi-freq rolloff to 0.25

Sort of makes sense to have these two be symmetrical

plugins/spectral_compressor/src/compressor_bank.rs

@@ -306,7 +306,8 @@ impl CompressorParams {
                 if param_id_prefix == UPWARDS_NAME_PREFIX {
                     0.75
                 } else {
-                    0.0
+                    // These basically work in the opposite way
+                    0.25
                 },
                 FloatRange::Linear { min: 0.0, max: 1.0 },
             )