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Forums     Plugins     BMS BMS channels in Logic Pro (AU)


I was very happy to discover BMS exists, as I need to create an LFE channel from a stereo mix (In Logic Pro 9.1.8, Mac OS 10.8.5) to send to a subwoofer, and then route the post filtered stereo L,R to the mains (with lows removed).  I want to use 3 outputs thru my audio interface for this, e.g., Logic outputs 3 and 4 as post LFE, high pass filtered stereo pair, and say channel 5 as LFE channel.

If I add BMS to the stereo mix buss, and select default mode as MOVE, and then set all channels to DEF, then I thought I would see the LFE content be removed from the stereo mix buss - which feeds stereo output (3,4), and I set the LFE channel = 5.  My interface does have 8 ins and 8 outs, and I have all the stereo output pairs visible in Logic's mixer for stereo pairs 1-2, 3-4, 5-6, 7-8.  But, I do not see any LFE signal being sent to channel 5 (nor if I change it to another channel besides 3,4) in Logic.

It also seems strange that when I pan the stereo signal hard left or right on the mix buss with the BMS Plugin feeding outputs 3,4 - with the default mode for all channels set to MON - I do indeed see/hear LFE content - but only when pan hard left but not when i pan hard right.  So it looks like BMS is only processing the left channel (and not the right channel) from the mix buss being sent to outputs 3,4.  I tried switching from a stereo to a surround panner on the mix buss with the BMS plugin, but it did not seem to make a difference.

If I read the other postings correctly, the HPF signal that would go back to the mains is always set to be at 80 Hz for MOVE mode, so I should pick 80 Hz as well for the LPF for the LFE to be symmetrical (with 12 dB filter slope for LFE) ?


BMS works in stereo in your case.  To work as expected you have to put BMS to at least 3-channel track.

"Works in stereo" means BMS does not even know about channels beyond L,R.

If I setup Logic for surround, and use a surround enabled buss (i.e., a buss with surround panner), and I assign the LFE channel in Logic's audio output I/O assignment window to say output 5, then it looks like BMS does output low frequency information to that channel.  But the output channel is controlled by this channel assignment in Logic - and not what I select for the index channel in BMS.  In this example, I have a stereo signal being sent to the surround buss (stereo input, and only the LFE enabled as the surround output) with BMS set to MOVE mode for channels 1 and 2.  But I still don't get why if I pan the stereo input signal to hard left - I still see output from BMS, but when I pan the stereo input to hard right - there is no longer any output from BMS.

The reason maybe that Logic still passes 2-channel audio to BMS.  You have to first convert stereo to surround and then use BMS on surround channel, without panner.

Yes, you are right.  I was missing that Logic has to be set to universal track mode in order for surround buss to work properly.  Once I did that, then both channels and panning of a stereo source work as expected, and BMS plugin works fine.  The only question I have right now is what I see when I run a sweep tone as the stereo source, and I monitor the high pass filtered left and right channels - and the LFE output on meters from the output of BMS.  It looks like the sweep peaks in the L and R mains before it peaks in the LFE channel, or the LFE looks like it lags behind the mains. (The LPF is set to 80 Hz, with 24 dB slope).  Maybe this is inevitable because of the filtering of low frequencies however?  Anyway, happy to buy the plugin, and I cannot believe that no one else makes this ;-)

This is inevitable as filters are not linear-phase.
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