Presonus BlueMax Smart Compressor - Blue-Max S21034 15 studio pre-sets: 3 vocal, 8 instrument, 2 classic stereo, 2 special effects "Squeeze Guitar" and "Pump" Manual mode gives you full control over compression parameters, including: variable input/output; Attack/release times and ratio from 1:1 to 20:1 Input/Outputs are 1/4" TS unbalanced Stereo/mono operation with high gain mono input for plugging instruments in direct Internal power supply