For the RCM-402 for a boosted frequency response at approximately 20kHz. Together with the standard grid and the PG-78 there now is a wide range of possibilities for acoustic equalizing the Sonodore microphones. The PG-88 delivers a virtually ideal frequency response with a slight boost of 2,5dB at 20kHz gradually coming down to 0,7dB at 30kHz which is often perceived as delivering a more 'open' sound stage. For use at greater distances then 1 meter this proves to be a very nice feature indeed. Many mastering engineers add this bit of 'top-end' in recordings... The Sonodore can add this now right at the source. All other qualities of the RCM-402 stay in tact, like the exceptional impulse response and omni directional character of the microphone