[Moderator note: Topic merged]
“Noise gates” are blunt instruments for bashing low level noise between tracks or audio clips.
In its simplest form it will allow sound to pass if the sound level is above a set “threshold” level, but when the level drops below the threshold the “gate” will “shut” and the audio will be muted.
NoiseGate version 2.2 has been tested with Audacity 1.3 only. Feedback from anyone that would like to try it out is welcome.
In this version there are 4 user adjustable parameters: Gate frequencies above: > If the Gate frequency is set to 20Hz, the full signal will be processed, otherwise only frequencies above the Gate frequency will be gated. This may be useful for reducing hiss between audio clips. Level Reduction: > This is the amount of reduction (attenuation) that will be applied to the sound when the gate is “closed”. Gate threshold: > When the audio goes below this level the gate will close. Above this level the gate will open. Attack/Decay: > This is the length of time that will be taken for the level fall to the attenuated level and to rise back to normal.
This noise gate uses “lookahead”, so when the gate is closed, it will start to open just before a sound that has a level above the threshold is encountered. This prevents the attack of percussive sounds from being lost as the gate will be fully open in time for the sound to pass through.
For anyone using Effect category grouping, the noise gate should appear in the “Dynamic Processor” section of the Effects menu.
This is “almost” exactly what I need, but I need a version modified to clamp to perfect silence, instead of just really really quiet, so that the “Detach at Silences” (a/k/a Disjoin in older versions) function will cause the quiet regions to go away.
I tried manually editing the .ny file to set the level-red variable to zero, and the result was almost perfect. When the gate closed, I got perfect silence, suitable for “Detach at Silences”, but the gate opening attack then included clicks at the beginning and end of the attack window (i.e. for a 250ms attack/decay setting, two clicks, 250ms apart). The clicks proved too annoying to tolerate.
Previously, I tried the included “Gate” effect, which was a little different. This one does produce “detachable” silence, but will hold open for at least a second past the end of the desired audio, and no combination of the attack/hold/decay sliders can make the gate close any faster. I’d like to have a gate that can than open and close quickly, produce high quality output, like “Noise Gate” does, but have the option to clamp to “detachable” silence, not just really quiet.
This will allow me to use the “Detach at Silences” function to quickly drop out the quiet portions below the threshold, and then I’ll be slide the remaining sounds around on the timeline with minimum fuss. Which is what I really need to do for my project.
Does anyone (the author himself?) know how the “Noise Gate” plugin might be modified to accomplish this?
I modified the code as you instructed, appending a note to the name to differentiate it from your original plugin, and tried it out. It perfectly clamped the regions below the threshold to perfect silence, allowing me to use the disjoin command to separate out the individual audio pieces for sliding about the timeline. This will speed my editing up greatly!
Thanks so much, stevethefiddle! Not being a LISP/Nyquist programmer, the obviousness of your simple code change was only apparent after the fact. I appreciate your effort!
This next bit is off-topic, but demonstrates a use case for Audacity. In case any reader my be curious what I’m up to, I’m using this with audio streams from the LiveATC.net archives. If you’re an aviation enthusiast, you might already know the site, which fosters a community of folks who capture and stream air-band communications from nearby airports. Students can find the site invaluable for learning how ATC controls traffic, and developing an “ear” for comprehending the often rapid fire instructions.
To follow the action where multiple control positions might be available for listening, it’s helpful to jump from channel to channel to hear how ATC commands manage the flow of individual aircraft. Often, communications overlap in time, so this modified filter allows me to build a timeline of several recorded ATC channels, and slide any overlapping individual transmissions to areas of silence in the other channels, while keeping relatively close to the original timeline. The project can then be mixed down into a single audio file, and you can then listen and build up a mental picture of the traffic being managed, and how ATC is guiding flights to maximize airport flow. This can be a helpful learning aid for student pilots who will eventually need add their voices to this din and understand and be understood by their fellow airmen.
Quite a lot of changes so we’ve skipped a version. Most of the changes are to the help files, but there are also a couple of significant changes in the code.
Gate to absolute silence:
This is the main new feature in version 2.4
To “gate to silence” set the “Level Reduction” to below -96 dB.
Due to the size restrictions on help screens in Nyquist, there are now 4 built in help screens. I’m quite tempted to rip them out altogether and just include a separate help text file. NoiseGate_version_2-4.zip (5.5 KB)
Noise gate 2-4 seems to work nicely: the hiss at the start of this recording is reduced …
Odd thing I noticed is the envelope of the “after” waveform looks slightly different from the “before” …
although I can’t hear a difference in the audio there are very slight changes in the before and after spectra of the speech.
NB: I did not select the “low cut”, which would affect the speech waveform,
the only operation applied was the noise gate which should not alter any of the speech, only reduce hiss in the “silence” at the start …
That’s because of the “Gate Frequencies Above” setting. You will always get that type of effect occurring when using frequency filters - perhaps it needs rewording to indicate that in most cases you would leave that set at 0 ?
No, the audible differences are much less than the visible difference because the visual difference is primarily due to changes in phase, whereas human hearing is relatively insensitive to the phase.
The audio above the noise threshold will be totally untouched if you are not using the filters (Gate Frequency Above set to 0).
Nyquist plug-ins are written in Nyquist code, with a simple graphical interface provided by Audacity (for more information, see: http://wiki.audacityteam.org/wiki/Nyquist_Plug-ins_Reference).
This interface is very basic and does not provide the ability to change menu presets. We are hoping for more versatile interface options in a future version of Audacity, but that is not likely to be in the near future unless we acquire a C++ developer that is particularly interested in developing this part of Audacity.
I don’t have a clue what I’m doing wrong, but no matter how I set the settings, I don’t get silence. I downloaded and installed the new version but still can’t get absolute silence like I get clicking the silence button. I feel stupid and frustrated. I assume this works but I can’t get it to work.