Gain Problems with Pro Tools and an SSL 12 Audio Interface – Solved

Paul, I’d benefit from another hour with you.  I have an imbalance in the left and right channel gain balance at the end of the SSL Fusion chain. Could you help me with this?

Last week I connected with a producer client, T, who I helped to set up Pro Tools in combination with hardware processing units. We connected again for a follow-up session to help resolve a problem which T had noticed in the setup.

T was running his stereo pre-master through an SSL Fusion as one of the steps in his mixing and mastering chain. The trouble was that there seemed to be a mismatch between the left and right levels when returned from the Fusion.

I started the investigation by setting up a test Pro Tools session. T and I talked through the chain of software and physical connections and made sure all the settings in Pro Tools were correct.

• Mono bass channel
• Outputting to Pre Master Aux track via Bus 1-2
• Outputting to Out 3-4 on the SSL12

• Out 3-4 of SSL 12 connected to Fusion inputs Left + Right via XLR cable
• Outputs Left + Right of Fusion connected to SSL 12 Analogue Inputs 3+4 via XLR cable
• Gain on SSL 12 Inputs 3+4 both set to line-level

Although everything in the chain looked like it was working, we could clearly see a difference in the left and right channels on the Record Master channel in Pro Tools:

Upon closer inspection, this slight difference was also shown in the SSL 360 software, but was harder to spot because of the meter scaling:

We then went through the process of trying to find the cause of the mismatch. We tested each section of the chain, swapping over XLR cables and Pro Tools I/O settings, checking on the results to see the difference after each changed variable.

After a while we found the cause of the problem: The SSL 12 had different gain levels on Inputs 3+4 despite the front pots being set to the centre detent.

Some research online led me to this Gearspace forum post where other users were having the same issue with a very similar SSL interface, the SSL BiG SiX

https://gearspace.com/board/electronic-music-instruments-and-electronic-music-production/1406378-ssl-six-stereo-channel-pan-unbalance.html

It looked like T’s SSL 12 was suffering from the same problem.

The solution was to make a tiny adjustment to the gain pot on channel 4 to compensate for the mismatch. Not ideal in terms of having to compensate for something that should have been spotted by SSL’s quality testing, but T was happy that he now had a working mastering chain.

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