Hum during playback

Hi Folks,
 
I seem to be having some problem with recording audio. Each time I record an audio track, and play back, I am hearing a light hum before the actual music is heard. In track view when I look at the particular track's meter setting, I notice that the level is up to -54, which of course is a very low level, even before the actual muic starts, meaning if the recording starts at bar 1, but I actually play my keybaord from bar 2 onwards, I expect silence, no hum whatsoever from between bar 1 to bar 2, when I playback. This was the case all this while, but now I am hearing a hum. Even during recording when I release my finger from the last note, the level drops to -54 and stays there!!! I am not sure why this is happening. My DAW is Sonar X1 producer and my  audio interface is Roland OctaCapture and my Keybaord outputs are connected to inputs 5 and 6  of octacapture (left and right respectively). Hope someone can advise. Thanks.
 
regards
glisando

Hi AT,
Thanks for the response. Yes I am actually trying to troubleshoot in that way. One thing I forgot to mention earlier was that my input selection in Sonar for the track in question was set to 'Stereo OCTA-CAPTURE IN 5-6' , that's how I always do my recordings from KB and I didn't have any issue.  What I did now was to plug out the cable from the 'right' output of my KB that goes into the 'input 6' of OC. Which means the connection from the left of my KB to 'input 5' of OC remains intact and I set the input selection in the track in Sonar to 'Left OCTA-CAPTURE IN 5-6'. I recorded and there was no humming issue, very clean. Now suspecting a cable issue, I replaced the cable with the one that I was using for 'right' input/out connections, and the input selection in the track in Sonar remains at 'Left OCTA-CAPTURE IN 5-6'. I recorded again and once again no issue, meaning both cables are fine. I repeated the same experiment this time with settings and connections for the right for each cable and once again I get a clean recording. I am still experimenting, but for now my impression is that I am getting this problem only when both cables are connected and the input selection is set to 'Stereo OCTA-CAPTURE IN 5-6', I am not sure why it has to be this way. I am begining to wonder if a factory reset would solve the problem in some way..mmm...

Try making sure your external gear (keyboard) is plugged into a grounded outlet on the same circuit as the A/D converter and Pre. This is assuming the keyboard uses a three-prong plug. Also make sure your DAW gear is all properly grounded. We need to be sure you don't have a ground loop. Also, ensure drivers are up to date, and you're using high-quality cabling. 

I could tell you how to ground such equipment, but can't be held responsible if implemented correctly and causing a fire. I do a lot of on-location recording, many times in places with poor or no grounding of outlets, so I have to run my own grounding in a case like that. 

Not sure this is your problem, but I have a similar set-up: Sonar X2, Octa-capture with keyboard on 5-6. For a long time I was trouble shooting mysterious noise in my system, sort of a hum with some computer type noises getting in there too. Tried EVERYTHING to isolate a ground loop with no success. Freakishly, unplugging the keyboard audio cables would cure the problem and running a ground from the back of the Octa to the computer chassis or the keyboard cables would partially solve the problem. Turned out the problem was that (somehow) the input levels for the unused channels in the Octa were turned up pretty high, introducing noise that was apparent when there was no other sound output. Turning the unused channels all the way down cured the problem completely.
If you actually have a ground problem you might experiment with using the ground on the back of the Octa to your computer chassis.

I've successfully cleaned up a similar problem by placing a stereo direct-box between the hardware synth and the audio inputs and utilizing the ground-lift switch on the direct box though this will decrease the overall input volume from the synth and on my setup, I'll set my motu gear's inputs to -10db(consumer) instead of +4(pro grade) to try and make up the lost volume.

Also, some hardware synths are just plain out and out noisy and the only real solution is to either use a noise gate (sonitus GATE w/standard gate setting and adjust the threshold to taste) or a noise reduction plug such as Voxengo's Redunoise which allows you to sample the noise during the silence and automagically removes the unwanted noise albeit with a bit of artifacting (I'm actually using BIAS SoundSoap but it is unfortunately no longer available).

Best,
guitardood