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Receiver audio filters
Squelch helpers, noise reduction and other filters that change only what you hear.
Press DSP on Home or on Scan to open Receiver audio. These settings change only what you hear. Recordings and decoders use the original sound. Some settings work only in some modes and are greyed out in the others.
Settings #
| Setting | What it does |
|---|---|
| Filter width | The width of the channel you hear, from Auto to 25 kHz. A narrow filter keeps a nearby station out. (Not on Scan, where each range sets its own width, and not in WFM.) |
| Passband shift | Moves the filter's passband up or down in steps of 10 Hz, to get away from a neighbour. Shown with the width. |
| Quiet until | A second squelch that listens to the signal itself. Off: Squelch slider only; A station transmits (like a handheld radio: silent until a carrier quiets the hiss, open through the pauses of an over); Someone speaks (only speech is heard; carriers, data and noise stay silent). A station transmits needs the NFM filter at Auto or 12.5 kHz and wider. |
| AGC | Automatic gain control, which keeps the volume even. Fast, Medium or Slow. |
| FM de-emphasis | Broadcast FM is sent with boosted highs. This undoes it. 50 µs: Europe, Asia, Africa. 75 µs: the Americas, South Korea. |
| Mute the buzz (digital voice) | Quiets the buzzing sound of digital voice signals, which the app does not decode into speech. |
| Clear voice (AM, SSB) | Makes speech easier to understand. |
| Remove hum | Takes out the steady hum of the mains and its tones. Works in AM, SSB and CW. |
| Noise reduction | One at a time: Off; Spectral (AM, SSB and CW); AI, light (little processing, works well on FM); AI, strong (more processing). The AI ones run on your phone. With a method on, Strength sets how much (0 to 100 percent) and Hold to compare plays the sound without noise reduction while you hold it. In CW, AI noise reduction stays off because it would take out the Morse tones. |
| Auto notch (ANF) | Finds a steady whistle or carrier tone in the signal and removes it. AM, SSB and CW. |
| Noise blanker (NB) | Cuts short clicks and pulses, such as ignition or power line noise. |
| Decode RTTY (USB / LSB) | Turns on the RTTY decoder. See RTTY. |
| Decode PSK31 (USB / LSB) | Turns on the PSK31 decoder. See PSK31. |
Tips #
- In FM, use the AI noise reduction: Clear voice, Remove hum, Spectral noise reduction and Auto notch work in AM, SSB and CW only.
- If you hear nothing, check that Quiet until is Off. See Troubleshooting.