DevOps, Sound Engineering and other things of interest...

Avid Eleven Rack Hiss Problem Solved

| Comments

This is a bit of a departure from the rest of my blog posts, as it relates to my main hobby and current interest – Bass guitar and amplification. I play in a band and have spent a lot of time building out my main rig for live shows and rehersals, but I recently ran into a problem with the latest addition. I found a solution to it (and lots of people suffering from the same issue), so I’m posting it here in the hope that it might help someone else.

I had just bought an Avid Eleven Rack modeller to replace a series of utterly unreliable Behringer V-Amps (that’s a story for another day!). It sounded great when hooked up to my computer as a recording device, but I had a major issue when using it through my power amplifier for live use. I was running the XLR balanced outputs to a Behringer DEQ2496 unit for final EQ tweaks[1],  the XLR outputs from that to a Crown "DriveCore" XLS 2000 power amp, and then finally into my two cabs.

However, despite using good quality cables and balanced links all the way through the signal chain, there was always a really annoying hiss present from the XLR outputs, even when I eliminated the Behringer unit and ran straight into the power amp. No matter what I tried on the 11R, this hiss was always there and could be heard when I was playing, and also when there was no input at all to the 11R, regardless of what patch I had selected – it sounded just like the general noise of the unit.

It wasn’t as noticeable on the "Output to Amp" sockets, but then those provide instrument-level signals, and the power amp expects line-level. This meant that if I carried on using those outputs, I had a marginal improvement in sound but at massively reduced volume – so I couldn’t use it live. If I was using a regular combo amp or head then it would have probably worked OK, but I needed to go through my power amp. Also, if I ever ran the outputs direct into a mixing desk, the problem would still persist.

As I mentioned before, I Googled for "Eleven Rack Hiss", and this showed many people having the same problem. I was about to give up on it when I then realised that the hiss didn’t seem to be present when recording (keeping the signal digital). So it seemed to be an issue solely with the analog XLR outputs, which tied in with the results of my Google search.

I then realised that both my R11 and DEQ2496 have digital AES/EBU connectors, so did the following :

  • Set the 11R clock rate to 96Khz (it’s in the User Options menu). Leaving at the default seemed to introduce odd artifacts and bad sound otherwise. Here’s where it is in the 11R’s menu when you hold down the "Edit" button for a few seconds (click any of the images in this post for bigger versions) :

  • Connected the 11R to the DEQ2496 through the AES/EBU ports
  • Set the "Digital Output" option on the R11 (see above image) to "Mirror Analog", so the "Output To Amp" option affects the digital signal as well
  • On the DEQ2496, switched the input on my presets to digital in, and checked they had locked onto the 96Khz signal:

  • Connected the XLR outs from the DEQ2496 to my power amp

Problem solved! I now have to control the master volume via the gain controls on the Crown power amp, but that minor change aside it’s working perfectly. No hiss whatsoever, everything is crystal clear (apart from the usual noise introduced by high-gain patches and so on), even at full bone-shaking volume. The difference is literally night and day!

So, it looks like a general solution is to take a digital output from the 11R, and feed it into a unit (such as a DEQ2496, or a cross-over such as the DCX2496) which has the appropriate outputs for your chosen power amplifier or PA system. I appreciate this probably involves shelling out for an additional bit of equipment – but if you’re planning on using an 11R through a power amplifier or PA for live use, then you may well find this makes all the difference to your sound.

Anyway, hope this helps someone!

For reference, here’s a slightly blurred picture of the rear connections so you can see how it all fits together :

In that picture, red bundled cables are power from the Samson power conditioner, green are MIDI cables, yellow is the XLR output to the power amp and purple is the digital AES signal. The stray ¼" TRS jack hanging out the yellow bundle is there if I ever want to plug the front "Output to Amp" socket into my practice Laney combo.

[1]=Really useful if you want to compensate for the sound of a venue, but don’t want to go through all your patches and tweak things. For instance, my band once booked a really bad rehersal space where my bass would make the room vibrate at a certain pitch. I simply dialed out the bad frequencies on the DEQ2496 and left all my presets as they were; crisis averted! Plus, it’s MIDI controlled so I can switch presets on that and the 11R with my FCB1010 pedal.