From c1c7190995de74c4505780f9dc09f02e705ecc06 Mon Sep 17 00:00:00 2001 From: Denny Sheirer Date: Sun, 3 Aug 2025 06:29:21 -0400 Subject: [PATCH] Updated Playlist Editor (markdown) --- Playlist-Editor.md | 22 +++++++++++++++++----- 1 file changed, 17 insertions(+), 5 deletions(-) diff --git a/Playlist-Editor.md b/Playlist-Editor.md index 4867729..39e61af 100644 --- a/Playlist-Editor.md +++ b/Playlist-Editor.md @@ -904,22 +904,34 @@ and have trunked system results in either the **County Trunked Systems**, or **S *** ### How To: Setup and Use NBFM Squelch -This guide describes how to setup an NBFM channel using the new FM power squelch feature. +This guide describes how to setup an NBFM channel using the new FM noise squelch feature. 1. In the Playlist editor, click the **Channels** tab 1. Click the **New** button and select the **NBFM** decoder 1. Enter a **Frequency** value in the **Source** section. 1. Select 12.5 or 25.0 kHz channel bandwidth. -1. Leave the **Squelch Threshold** setting as is, for now. 1. Click **Play** button to start the channel. 1. Switch to the main sdrtrunk window 1. Select the channel that's playing in the **Now Playing** window 1. Click the **Channel** tab in the lower section. -1. Adjust the **Squelch Threshold** (blue line) up or down so that it's slightly above the current noise floor represented by the solid grey bar. Monitor the channel to ensure that when the signal is active it exceeds the threshold and you hear audio. -Note: the noise floor changes each time you change the gain settings or sample rate of your tuner and you must adjust the squelch threshold with each of those changes. +The noise squelch view contains the following controls: +* Slider: noise open threshold. +* Slider: noise close threshold. +* Slider: hysteresis open threshold. +* Slider: hysteresis close threshold. +* Override Button. Disables the noise squelch control and passes all demodulated audio. +* Reset Button. This button resets the noise and hysteresis sliders to their default values. -![image](https://user-images.githubusercontent.com/4079756/159229963-f4d990bb-ef2f-4193-b02c-cda3921cdcbd.png) +#### Operation: +* Concept: the noise squelch control operates on the 'quieting effect' of FM modulated signals. When transmitting, the noise level in the FM demodulated audio is greatly reduced and the transmitted audio is usually in the range of 0 - 4,000 Hertz. When there is no signal present, the FM demodulated audio is filled with random noise. The squelch control measures the statistical variance of the demodulated audio in 10 millisecond windows and then compares the variance against the open and close thresholds to determine when to open and close the squelch. The squelch control uses an audio buffer longer than the open and close hysteresis duration thresholds to ensure that no audio is lost while calculating when to open or close the squelch. + +**Note:** the noise squelch view displays the channel noise in the range of 0.0 to 10.0. When a signal is present, the noise level will be displayed as a value close to 10.0 and it will display a randomly changing value in the range 2.0 to 6.0 when there is no signal present. The actual noise values used in the squelch control range from 0.0 to 0.2 for a signal (ie quite/minimal variance) and 0.2 to 0.5 for no signal. This conversion of actual noise value to displayed noise value is intentional to align the visual representation of the noise and hysteresis values on the X/Y graph/chart and present the information in an intuitive display where both values transition from low (no signal) to high (signal present). + +* Open Squelch: the audio squelch will open and pass audio once the noise level is above the noise open threshold for a combined period of time that is longer than the hysteresis open threshold. The hysteresis value is units of 10 milliseconds. +* Close Squelch: the audio squelch will close and mute audio once the noise level drops below the noise close threshold for a combined period of time that is longer than the hysteresis close threshold. + +NBFM Noise Squelch screen capture ### How To: Use Aliases With NBFM Decoder This guide describes how to setup the NBFM decoder so that a static talkgroup value is assigned to each audio segment generated by the NBFM decoder so that you can take advantage of sdtrunk aliasing features like streaming and recording with NBFM audio segments.