Lost your Felt Treble Filter inserts? Don’t worry we’ve got you covered. Use these F.T.F inserts with your Monitor headphones whenever you want your sound to be laid back and warm. To really hear those higher-than-human highs, just leave your F.T.F. inserts out. Never noticed our Monitors even come with this feature? Ok then let us explain a bit more. With the F.T.F. snugly in place you’ll notice the Monitor provides a smooth warm bass feel to your music. Pull off the magnetically held in place ear cushions then slip out the F.T.F. and you’ll find your Monitors instantly produce a more dynamic and brighter sound.