How to Make a Multiband Tube Compressor in Logic Pro

Logic Pro hasn't got a dedicated multiband tube compressor plugin. There was some speculation that the same compressor circuit type options found in Logic's standard Compressor plug-in would be added to the MultiPressor in version 9, but it was not to be. Maybe in Logic Pro X? In the meantime, you can construct your own using Auxiliary channels. Maybe it's not the quickest way to create a signal processor, but you might be more likely to understand what it is actually doing! 

The idea behind multiband compressors is that you can apply different compression settings to different frequency bands, and in the case of one built with vacuum tubes or valves, each frequency band can take advantage of the unique sonic characteristics that these components can lend to a sound, especially when driven hard.

Creating a Multiband Tube Compressor with 3 Frequency Bands:

1. Add three stereo auxiliary channels by clicking the '+' button on the far left of the mixer (choose the first available bus as the input, and tick the 'Ascending' box)
   
2. Set up a send to each auxiliary channel from the channel that contains the file you are mastering
   
3. Set send levels to 0dB by Option-Clicking on the send level
   
4. Add a low-pass filter to the first Aux channel (the low end signal), and a hi-pass filter to the third Aux channel (the top end signal) and set the cutoff points to taste
   
5. Add a High Cut and a Low Cut filter to the second Aux channel (the mid-range); this is in place of a bandpass filter which Logic does not provide. Set the cutoff points to coincide with those in the lo and hi-pass filters
   
6. Add Logic's Compressor plug-in to each auxiliary channel (after the filter)
   
7. Set each compressor to the circuit type of your choice (see below)
   

Now you can make appropriate settings on each compressor: a parallel compression approach is to set the threshold low and the ratio high to create desirable distortion artifacts, then mix these in with the uncompressed signal using the auxiliary channel output faders.

Multiband tube compression with three bands.

As an alternative to the use of filters to control the frequency bands, you could use MultiPressors as filters (one in each Aux channel), by soloing the applicable band in each instance of the plug-in, and setting the compression ratio in the MultiPressor to 1:1 so that compression is handled by the Compressor plug-in instead.

Multiband tube compression using Multipressors as filters.

Although there is no information provided in Logic's documentation, there appears to be general agreement that the Circuit Types in Logic's Compressor are intended to emulate the following classic compressors:

• Platinum: Emagic's own compression algorithm
  
• Class A_R: Neve 2264/33609; the R is for Rupert. This would be vacuum tube style compression
  
• Class A_U: Vari-Mu e.g. Fairchild 670/Manley. Again a vacuum tube emulation, but designed to be more transparent than the R.
  
• VCA: DBX 160/SSL G-Master buss compressor
  
• FET: Urei 1176 or similar
  
• Opto: Teletronix LA2A or similar
  

Find out more about Logic's Compressor and MultiPressor in Logic's Mastering Toolbox and Olav's Electronica Workflows tutorial.