Hi, how would I go about using Renoise’s native efx to process the master output so that everything below 130hz is mono, please?
maybe, with the *multiband device ?
use the track scopes view and TURN OFF the 2 last send tracks ; you’ll see that the lower bands are in mono
That is not possible. You need to split the bands into sends first.
(I use Tone Projects “BassLane” plugin for monoing below threshold in a fast way)
so basically i’d be using a multiband on a drumbeat + bass, only send below 150hz stuff to the send, and use some utility inside renoise to switch that send to mono? is that possible within native renoise?
(the drumbeat+bass trax would of course use a multiband that mutes that band which has been sent to be mono-ified, im guessing)
That’s very possible. Use the “stereo expander” to mono the send having the low-band signal.
Not the answer you want, free native solution, but I’ve heard good things about:
is that “safe”? come to think of it, is “multiband send” safe?
i.e. if i start using it and invert the result and play both together, will they be completely canceled out or is it basically untrustworthy for quickly delivering a finished wavefile to the mastering engineer?
Try it out, or render two versions, one without the effect and one with the effect.
Create a send track #1.
Put the multiband device on this first send track #1.
Set the first band of the MB device to 130Hz or 150Hz for example.
Create other send tracks #2 #3 & #4 and link the multiband device to these new send tracks.
A add a stereo expander device in the send track #2.
You’ll see in the presets of the stereo expander that you can turn everything to mono.
Then compose your music using normal tracks.
Once it’s finished you send every normal track to your send track #1 where you’ve put the multiband device.
Then play your music.
If you want to see if this works for your needs, use the track scopes view while playing your music and click on send track #3 & send track #4 to turn them off. You’'ll easily see that everything is mono on your headphones.
The only way for you to see if the multiband device works or not, is to test it.
If you don’t want to use this device, believeing it’s not “safe” then try to use my multiband device emulator located in my signature.
When you split a signal into multiple bands, then apply unique processing to each band, and then mix it all back together, there’s always a chance that you will affect things in some way. You might get a small amount of sound cancellation occurring where each band overlaps, but it really depends on the extra processing you do. For example, if you split off the mid/high frequencies to apply some chorus and reverb, then mix that back into the mono’ed low frequencies, you might get a small amount of “smearing” where the frequencies overlap, but it should not be too serious. Just be careful, take your time, make gradual changes, check the results, etc.
The Stereo Expander is doing nothing special really.
When you set it like this ^^^ then it will simply mix Left and Right channels together into a mono signal. The result is exactly the same as if you had manually done this yourself using other techniques. There’s no voodoo magic or special algorithms taking place here, so you can for sure safely use this to mono your signal. In fact, it will quickly reveal any phase problems when you do so, because you will typically notice quite a big drop in volume if you mono mix a stereo signal that is badly out of phase, since the Left and Right channels will cancel each other out a bit. So if you mono your bass and you don’t hear a big drop in volume, then you’re already on the right path 
The Multiband Send is actually a lot safer than the old technique of doing it manually. The filters in the Multiband Send are designed to work best in these situations, with as little overlap and phase distortion between bands as possible. When doing it the old way (even with the very steep Butterworth 8n) you can still get a small amount of overlap, and therefore you can run into problems more easily.
This! This helps soooo much!! 
.
Got a 5 paragraph email back from a mastering engineer who was asking me to do something about
-phasing, some sounds only being on the side and nothing in the mid ((it’s interesting that KMaki has done some work relating to mid-side-tools for Renoise, on a Renoise-related no))
-overall 70hz boxiness on the bass and also the drums being too far away in the mix resulting in issues when playing on heavy duty rigs
-how some elemenets would vanish completely when played on any mono device (rig,broadcast,etc)
then he linked a pc+osx free vst tool for doing the stereo->mono, which is around after which i came here.
either way, since the Stereo Expander does not allow for it’s 3rd parameter to be toggled (Left,Right,Left+Right), only the first two are named in ```
rprint (renoise.song().selected_track.devices[2].parameters[1].name)
Expand
rprint (renoise.song().selected_track.devices[2].parameters[2].name)
Surround
There was some strange behaviour noted when Multiband Send was used on a Send Track, rather than a “Normal” Track. Not 100% sure if this has been cured but there was a long discussion on it, which also culminated in the slopes of the filters being changed. I’m not sure if it was only if using multiple MultiBand Sends into each other but I think similar was noticed whenever it was in a Send Track. I know a lot of it related to a 180deg phase shift on the mid-band/at crossover points.
But, although the waveforms looked very different in the tests I personally found it about impossible to hear the difference. When using square-waves as test source there was a lot of overshoot and ringing, which will eat badly into your headroom, but these effects you expect to see to some extent or another with LPF (and to a lesser extent HPF) and you are not going to Mono one group of frequencies without filtering.