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The "DSP Noise reduction" "Notch2" and "High Boost" features

"Autonotch" is now "Notch1"

The filter that had been labeled "Autonotch" is now "Notch1".

Unlike the new "Notch2" filter, this "Notch1" filter operates on the server side of the signal path and its operation can reduce the strength of strong CW notes (carriers) and reduce the S-meter deflection and prevent AGC action on that signal.

Unfortunately the original "Autonotch" notch filter (a.k.a. "Notch1") is susceptible to other strong signals meaning that it can be prone to "hunting" in the presence of strong modulation - and with weaker signals, it may not reliably "lock" on CW notes at all.
New features:   "DSP Noise Reduction", "Notch2" and "High Boost"

Operational notes:

DSP Noise reduction:

Also added is a noise reduction filter that can take out some of the background "hiss" and improve the signal-noise ratio.  This is the same type of filter may be found on nearly all HF transceivers these days:
"I reloaded the page, but DSP noise reduction (or related option) suddenly isn't working"

There's a quirk related to the "tick" boxes and drop-down settings on the WebSDR - and other similar boxes on other web pages and that is that if you reload or refresh the web page, the boxes or selections may look as though they are active, but they will not be.

For example:  If you were to select a DSP setting of Low, the DSP noise reduction would start working - but if you refreshed the page, it may still show that selection, but the DSP noise reduction would not be active.

The work-around is to select Off (or any other setting than the current one) and then select Low again to reinstate the filter.

This same quirk applies to practically every option on the WebSDR page from the frequency to the waterfall setting to the volume setting - and everything in between.  This is not a bug per-se, but just the way the HTML/Javascript that is being used works.

There are currently four settings for the DSP Noise reduction filter:
A few comments about DSP noise reduction:

DSP noise reduction works by quickly "locking on" to the voiced elements of human speech and filtering out the rest - and this works because voiced human speech consists of tones.  For signals that range from good to "moderately" noisy, this works quite well - but when signals are very weak, it may actually reduce intelligibility in some cases because the "tones" of the speed are increasily difficult to discern from the background noise.  When only noise is present or signals are very weak, the noise reduction tries to lock on to the random elements of noise causing the "swishing" (or "voices in a barrel") effect.

Because of its nature, this filter will also "lock on" to tones and it may be useful for CW use in some cases.  Note that this filter is adaptive and it takes time for it to "lock" onto a signal - and the higher settings take even more time to do this, so it may not be the best choice for rapid-fire contesting.

For casual listening, the Low setting is recommended as its effects are moderate, offering reasonable noise reduction without being too strong or causing deleterious effects on weak signals.

It is recommended that DSP noise reduction be turned OFF if you are trying to use any digital mode - and this is true not only for the WebSDR, but for ANY radio with DSP filtering.

The "Notch2" filter:

This filter uses digital signal processing techniques to detect a coherent signal - like pure tone like a CW note (carrier) - and block it out.  Because it is in the audio path its action will have no effect on the S-meter, but is may be more effective in removing weaker carriers that may still be annoying, but too weak to be reliably locked onto by "Notch1".  For very strong interfering signals you may wish to use both Notch1 and Notch2.

Of course, one should not try to use any notch filter with CW or digital modes as this filter's job is to remove the very signals comprising such signals!

The "High Boost" setting:

This setting boosts the high audio frequencies by 6 dB with the "knee" of the upward curve centered on 1500 Hz.  The purpose of this setting is to boost the "highs" which can boost the intelligibility of speech.

This feature may be helpful if you are using a higher setting of the DSP noise reduction, or you may have age-related hearing loss.


Any problems that might be caused by these features?

The DSP Noise Reduction, Notch2 and High Boost functions are client side - that is, they are run on your computer rather than the WebSDR server itself.  What this means is that they will increase processor load on your end - something that may cause intermittent audio issues on slower computers - particularly if you have minimized the browser window in which you are running the WebSDR.

It has also been observed that in general, the Firefox browser seems to work better than most other browsers.  The Chrome browser seems to have more trouble on some computers running the WebSDR's web page, causing issues such as audio drop-outs.  If this happens, check to see if the sound card's speaker output sample rate is set to 48000 Hz (in Windows) rather than something higher like 96000 or 192000 - or simply try using FireFox.


Where did these features come from?

These added features (DSP Noise Reduction, Notch 2 and High Boost) have been added to the client side of the code, written by the folks at the Northern Utah WebSD and not with the direct participation (but with the knowledge of) the original author of the WebSDR software, P.T. de Boer, PA3FWM.

If you have questions about these added features,  or if you operate a WebSDR system and are interested in adding them to your system please direct inquiries to  sdrinfo@sdrutah.org  and not PA3FWM, the original author.  


Bug fix:


There was a bug fix applied on 16 April, 2020 that fixes an issue where activating the squelch and DSP noise reduction at the same time could cause the Javascript interpreter to slow down (e.g. waterfall slowing, squelch may take a long time to open, buffer taking a long time to clear) when the audio was muted by the squelch.  If you have installed the DSP in your own WebSDR and have this issue, please inquire at the email address, above, for details of the patch.



Additional information:

Go to the Northern Utah WebSDR landing page