Invisible design: F20D1 is an invisible deep-in-canal hearing aid, using precision acoustic devices, providing a sophisticated design, invisible to wear Advanced sound processing: Using 16-channel WDRC digital chip for precise sound processing Excellent sound quality: Enjoy excellent sound quality with 16-channel low-level expansion, maximum output tone control and 64-band equalizer Intelligent noise management: Achieve clear conversations with intelligent background noise suppression and adaptive feedback management Convenient adjustment: Easily adjust the volume and switch programs with the multi-function button and volume adjustment key Rechargeable function: Powered by lithium battery, it provides long use time and fast 2.5-hour charging time to ensure uninterrupted hearing support Specifications: 90dB output sound pressure level: maximum: <114+3dB / average: 108±4dB 50dB saturated output sound pressure level: maximum: 30±5dB / average: 27±5dB Frequency range (Hz): 250~5000Hz Harmonic distortion: 500Hz: 5% / 800Hz: 5% / 1600Hz: 5% Equivalent input noise: 32dB Working voltage: DC 3.0~4.2V Charging time: 2.5 hours (zinc-air battery) Battery capacity: Charging box: 200mAh, hearing aid: 15mAh