<A bit OT> Sonar and hardware summing

Hi folks,
I know there have been some posts in the past about summing mixers/boxes and Sonar and I've been putting in some time trying to discover if there was really any "there" there (so to speak). I've gotten some interesting results and thought I'd share with the board what I've done, how I set it up and what the end result is.
 
Without going into too much detail, summing mixers are hardware devices that have no or very minimal controls.  The theory is that the process of taking the analog channels of a mixer and combining them into a sinlge stereo track (summing) has a particular, and in many cases desirable, effect. That theory led to the prodution of a bunch of summing devices like the dangerous music d-box.  After some reading I wanted to find out what this was all about.  So, that said, here's what I've done:
 
I have a pair of channels coming out of my Lynx Aurora interface that go to two places (via a patchbay).  One is my mains, the other is a pair of input channels on an SSL X-Rack 4 channel input module.  That input module takes the signal and passes it to the master module which then goes out an insert into a SSL X-Rack bus compressor and an SSL X-Rack Stereo EQ before coming back in the master module and finally out the record bus.  The record bus then goes into two input channels on the Lynx.  For this purpose the EQ and compressor have been disengaged, that is, the "in" button is not depressed so that they are not affecting the sound other than by having it pass through.  So the signal chain looks like this:
 
Lynx out -> SSL input -> SSL Master -> SSL Compressor (disengaged) -> SSL EQ (disengaged) -> SSL Master -> Lynx In
 
I wondered if this setup affected the sound and if so, in what way.  To test this I took a short drum phrase played with Jet City Drums and recorded it out of Sonar, through the SSL box and then back into Sonar. I then bounced it to a track without passing through the SSL box and then compared by ear and with an analyzer.  The results are interesting.  You can grab both wav files here:
http://www.xmission.com/~razorwit/SSL/SSL.zip
You may want to have a listen before reading any further so that my opinions don't affect what you hear.
What I heard was a change in the bass frequencies when passing through the summing box.  It seemed there was a tonal shift and some volume change.  It also seemed like the bass was a bit smoother (yeah, I hate that term too but it's the only descriptor I can think of) in the SSL version. To test this I isolated the kick and did the same thing, only this time I used the analyzer to compare.  Have a look at the frequecy plots below:
 

 
Notice that in the SSL plot (the top one) the very low freqencies (about 35 hz) are increased and then there is a dip in the 40 to 80 range. Also, the SSL box seems to cut a bit of the mid and high frequencies (above about 640).  I was sort of both right and wrong in what I was hearing.  I think the tonal shift was correct, but what I heard as smoother and louder bass was actually a dip in the 40 to 80 region and that lower bump along with the lower frequencies being emphasized when compared to the higher frequencies.
So, my conclusions, at least from this test: 
Is there a difference in sound when passing through a summing box, at least for this case?  Yes. 
Was it a big change?  Not really, but certainly not negligible.
Is it a good or bad change?  That's waaaay to subjective and really up for opinions, but it is interesting. 
 
What I'm really curious about next is what that tonal effect sounds like when it is additive.  This was a very simple test that only measured what signal passing through two channels of my SSL box does.  The real question is what happens when I have 12 channels passing through it and being summed instead of just 2.  Sadly, that will have to wait until I can afford an 8 channel input module, and right now is not that time....though if anyone wants to send one my way let me know! :)
 
Anyway, there it is.  Hope you folks find this as interesting as I did.
 
Dean

Jeff the only problem I have with your post is the repeated misspelling of Color. LOL

Hi Jeff,
thanks for the comments. In retrospect, this probably should have gone in techniques.  My apologies.
 
A couple quick notes.  I'm trying to be fairly careful about staying away from subjective analysis like "superior" and "inferior", but if I've managed to do it poorly (which is entirely possible), I do want to say that I'm really not making any statements about better or worse here, only different.  In fact, I'm still not particularly sold on the usefulness of the sound imparted by the SSL, but it's an interesting potential tool. 
 
Beyond that, just a couple other notes.  Regarding transformers, I suspect you're correct that at least part (and probably closer to all) all of the audio difference is due to transformers.  It certainly has what I think of as that "transformer sound" (though I don't know the specs of the SSL modules to say for certain).  However, the presence of transformers certainly does not mean that it's not a summing box.  SSL is quite clear that the intent of their 4 and 8 input modules is to build a summing box, and other companies have also made summing boxes with transformers...the Neve 8816 comes to mind here. I think there may be a good distinction between this and passive summing though. Regarding only two channels, I deliberately did that in order to reduce to basics.  I don't doubt that the results may be different if I was summing more channels, but for this I was interested primarily in the sound of the hardware. I'm also curious what it will sound like with 12, but that will have to wait.
 
Oh, and thanks for the link to the other discussion.  I'll have a look a bit later tonight.
 
Thanks again
Dean

Hi AT and Bit,
Thanks for the responses.  I think it's probably a point well taken to discern between the process of summing and a summing device.  If I read you correctly, the distinction here is that even though this was going through a summing device, there wasn't much actual summing (the process) going on, and thus what I was testing above is a summing device, but potentially not (much of) a summing process.  This is a good point and I'm actually curious to test it once I get a few more inputs to the SSL box.  My suspicion is that if there is a particular sound to the summing process (and that's a big "if"....I think I remember the SOS article you're talking about AT and I think I'll probably have the same result), it it's probably more apparent the more sources you sum, but having no direct evidence to back that up that's something that I'll have to try out...that's half the fun after all :)

Oh, one more thing.  I need to go and correct my OP, but I found out that the compressor and EQ were not inline after all.  I was recording off the record bus, and the master module insert loop isn't inline with the record bus.  So my SSL chain was only:

Lynx out -> SSL input -> SSL Master -> Lynx In

I had thought that the effect modules were coloring the sound even disengaged, but with them out of the chain it means that only the input and master module were coloring.  Well...and the Lynx Aurora, but they're awfully clean...

Anyway, thanks again for the comments.  I must say that I've enjoyed most of the other stuff that the participants on this thread have posted over the years, so it's nice to have comments from you guys on this.  I appreciate it.

Dean