cumbria designs





Minifilter DSP Audio Processor


A DSP Filter module with Auto-notch, Denoiser and AF Power Amplifier


The Minifilter kit assembles into a compact versatile audio processor with many uses. It's compact size and simple control interface make it a flexible solution to many audio filtering problems. Typical applications include an internally installed enhancement to a receiver, an amplified filter unit installed in a loudspeaker enclosure or a stand alone in-line filter unit.

Minifilter Kit

The Minifilter is supplied as a kit and comprises of a single PCB populated with standard through hole parts. The kit is easily assembled by anyone experienced in soldering and having the ability to follow written instructions.


  • 501 tap "rectangular" bandpass FIR filters (no ringing) arranged in two groups of 6 filters each;
    Wide Group Narrow Group
    300 - 2700Hz 400 - 900Hz
    300 - 2400Hz 450 - 850Hz
    300 - 2200Hz 500 - 800Hz
    400 - 2200Hz 600 - 800Hz
    400 - 2100Hz 500 - 700Hz
    450 - 2000Hz 400 - 600Hz
  • 11kHz sample rate
  • LMS Auto-notch
  • LMS Denoiser
  • Simple control interface to allow switch or logic control
  • LM380 AF power Amplifier


  • Size W66mm, H47mm,  D22mm
  • Nominal +12v operation (+10v to +20v)
  • 54mA typical current
  • High quality double sided silk screened PCB
  • Comprehensive 14 page instruction manual Ahora disponible en español Gracias a Jon Iza, EA2SN para la traducción!

Note: AF gain pot and control switching not provided with the kit as these will either exist in the target installation or will be selected to suit an application.

Audio Clips

The following audio clips were made by placing a PC microphone near to a loudspeaker connected to the Minifilter output. The audio source was an FT817 with the Minifilter plugged into the headphone socket. The antenna was a short loaded whip. Whilst the quality is not as good as it could be, the recordings provide a good indication of the Minifilter's capabilities.

CW 200Hz Switching filters from wide "pass through" mode down to 200Hz, (the clunking in the background is the test rig's rotary switch!)

Denoise 1, Denoise 2, Denoise 3 Denoiser on 40m voice.