"DSP Noise Reduction" and "Notch-2" features
New features: "DSP Noise Reduction", "Notch-2 and" and "High Boost"
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:
- It can reduce the background hiss on medium to strong signals: Reducing this hiss can reduce fatigue.
- Weaker SSB signals may benefit from noise reduction to improve intelligibility.
- The readability of CW signals may be improved by the nature of the filter to converge on coherent signals (like CW notes) and reject noise.
- Like any filters of this type, it probably will not help with signals that are very weak and "in the noise".
- In the presence of only noise, this filter will cause a "hollow" barrel-like sound: This is normal and is the nature of the filter.
If you have problems with "Notch-2" and/or "DSP Noise reduction:
The "DSP Noise Reduction" and "Notch-2" features should be considered to be EXPERIMENTAL: They are still being tweaked for performance and they may be buggy - that is, they may crash or do something unexpected, such as cause odd distortion.
If something happens, it will probably resolve itself in a second or two - but you might try turning the filter Off and then back on - but if that doesn't work, reload the web page.
If you experience such issues with these new features, please note what was
happening at the time (browser type, operating system, band, settings, frequencies, etc.) and send an email describing your observations to: firstname.lastname@example.org
Note: The "low" setting is a bit less agressive - appropriate for strong-medium strength signals with low-moderate noise while the higher settings are a bit more adaptable, improving their usability somewhat on weaker signals.
There are currently four settings for the DSP Noise reduction filter:
Low. The noise-reduction effects are fairly light and is probably the best choise for casual listening.
Medium. This has stronger noise-reduction effects, but more apparent artifacts, particularly on background (white) noise when no signals are present in the form of a "swishing" sound.
High. This has even strong noise-reduction effects: It may or may not help with intelligibility
Strong. This filter is designed to have even stronger noise-reduction: Its adaption rate is quite slow compared to the others, but it can be fairly effective in some cases. This setting often tends to make audio sound a bit "quieter" and cut the "highs" a bit.
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 "Notch-2" filter:
This filter, recently added, uses digital signal processing techniques to detect a coherent signal - like a CW note - 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 "Auto-notch" (Notch-1). For very strong interfering signals you may wish to use both Auto Notch and Notch-2.
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!
Any problems that might be caused by these features?
The DSP Noise Reduction and Notch-2 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 WebSDR 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 email@example.com and not PA3FWM, the original author.
These new features are not available on the "mobile" version of the WebSDR pages in order to allow their use on the widest variety of mobile/portable devices.
These features are also not in the audio path for audio recordings made using the WebSDR's "record" feature.