Summing Engine

[johndev]

I did a null test of Mixbus and Ardour. There is a slight difference but nothing that would be heard I believe. The null difference is about 80dB lower.

How I tested it using a set of multitrack stems:

1. Import stems into Mixbus, group and route sets of tracks through four mixbusses (drums, bass, vocals, rest), all pans centred, turn off all compressors/EQ/drives including master limiter and its drive down all the way. Master fader at -10, all others at zero. Export as 32bit float.
   
2. Import stems into Ardour, all pans centred. Master fader at -10, all others at zero. Export as 32bit float.
   
3. Import exports into new Ardour session. Phase reverse one of them.
   

If they were identical then there should be nothing heard. But I did hear something at a very low level. Turning up my headphones all the way it was still low but loud enough to hear what it was. It sounded the same as the mix but a bit crunchier, saturated? 

Turning the Ardour one's fader down by super small amounts made the sound start to disappear. By -0.066 I couldn't hear anything, headphones still at max.

Using the Export Audio Files > Only Analyze tool I checked the Peak and [Integrated Loudness] measurements:

• Playing just the Mixbus one (Ardour one muted) = -3.5 dBFS [-22 LUFS]
  
• Both playing, both faders at 0 = -45.7 dBFS [-63.8 LUFS]
  
• Both playing, Ardour fader at -0.0675 = -83.3 dBFS [LUFS could not be measured]
  

Using the above with different fader adjustments around the -0.066 mark showed that -0.0675 was the sweet spot, the biggest cancellation.

I confess to being a bit muddled on what this means so please somebody correct me if I'm wrong:

The only audible difference between the two is that the Ardour one was 0.0675 dB higher in overall gain. Reduce it by that amount and there is no audible difference. Whatever difference there is is ~80dB lower than the signal itself, so would never be heard underneath that signal, indeed could not be heard at all on its own with my headphones on max.

Meaning that the Mixbus summing engine doesn't colour the sound in any way that can be heard. Nor does anything else in Mixbus other than EQ, dynamics and saturation.

I wasn't game to try panning anything. I guess some hard left/right panning would have been fine but anywhere in between would have skewed the results because the two DAWs use different implementations.

[Holger]

Thank you johndev for your tests. IMO this is a common misunderstanding for Mixbus. It does not and should not colour anything if all faders and knobs are in zero position. That's the big advantage over analog consoles: You can have an uncoloured sound.
However, by default, the tape drive knobs in the buses are half way up and this of course colours the sound. And if you add EQ, compressor, gate or limiter this will colour the sound.

[Robomusic57]

Holger that was a question in my mind. The knobs are half way up i noticed that. Is halfway null, and lowering it detracts, and raising adds? interesting question. Or is the halfway part of the Harrison thing?

[johndev]

IMO this is a common misunderstanding for Mixbus. It does not and should not colour anything if all faders and knobs are in zero position.

I think the misunderstanding is, er, understandable. Generally speaking, analog hardware does colour the sound: warmer, fatter, etc. due to non-flat frequency response, harmonic distortion, and so on. If a piece of software says it emulates a piece of analog hardware then, on the face of it, the obvious conclusion is that the software colours the sound. But that is assuming that the hardware in question does colour the sound. From what Ben is saying in the other thread, Harrison consoles don't, and therefore neither does Mixbus.

So then the question becomes: what does "analog" actually mean then, for Mixbus. And that is what Ben is addressing in the other thread, also covered in this thread.

Holger that was a question in my mind. The knobs are half way up i noticed that. Is halfway null, and lowering it detracts, and raising adds?

All the way down = no saturation. The same as turning off the drive buttons which v9 now has.

Half way = some saturation. Which is what Holger is saying, that by default they're all half way (and on) so every mix will automatically be coloured by these drives, until you turn them off.