High Frequency noise in the D8b

[Old School]

Hi all,
Over the last few months I have periodically detected a high frequency "buzz", for lack of a better word, in some of the vocal tracks I have recorded. When I mentioned this to the customers while listening back to the tracks, none of them could hear what I was talking about. It almost sounds like distortion because it is more prevalent in the louder passages, but the levels I record at are nowhere near clipping ( under -18db). Fast forward a couple of months to some sessions for a hispanic band that has me do their tracking and then send the files for mixing to a studio in Mexico. I have done this for them several times before with no problems, but this time their guy immediately complained about a high frequency noise in the tracks. First I thought I would check my cables, no go, no matter what cable I use the noise is the same. So then I tried different mics, the Neuman, the AKG C-414, the Rode, ......same noise. Ok so now I'm thinking maybe its some thing in the phantom power so I plug in some sure beta 58's,....same noise. So then I think maybe its the preamps, so i plug in to the insert returns and bypass the preamps,...same noise. So now just to eliminate the HDR , I eq the noise completely out of a recorded track ( its 8.4k to 10.1k) and bounce it to another track on the HDR, and when I play back the bounced track , no noise. so I think it's safe to say the HDR is not part of the problem. So now I'm thinking wordclock? I try it with the D8B as master and with the HDR as master. same noise. I change the apogee word clock card, same noise. Then I think, maybe the electrical power? But when I sit there with the mics on and crank the gain WAY up, there is silence...... dead silence, if there was some kind of power grid hum wouldn't it be in there all the time? When listening closely its almost like a gate opens up on the louder notes and lets this noise though, and it doesn't sustain for the whole length of the loud note but fades out. I even went back to Version 3.1 of the OS just to see if It was something corrupt in the OS, .....same noise. Ideas anyone?

Have a blessed day,
Mike

[Phil.c]

That's a difficult one?
Have you tried recording just an open mic, also a clean guitar through the same input?

[doktor1360]

That's a difficult one?

I'd have to agree, Phil...

When listening closely its almost like a gate opens up on the louder notes and lets this noise though, and it doesn't sustain for the whole length of the loud note but fades out. I even went back to Version 3.1 of the OS just to see if It was something corrupt in the OS, .....same noise

That's most likely where I'd start Mike, it seems to be pointing at something in the hardware layer... especially if it's occurring on a consistent basis. I personally find the clocking of these mercurial consoles maddening, but I digress. Not only that, but you've indicated it's present across the OS layer (v3.0 vs v5.1) Even if not consistent in any way, it's possible to be indicating something that's thermal-related... ie. a component heating up. Does it appear present right after booting your gear up? Or does it develop (consistently) over a particular time, or do things appear to be completely randomized? Just some questions I'd ask myself that I feel need to be asked that might lead to more questions and/or something else entirely is divulged. But it seems you've really done a good bit of the triage 'homework' (checking cabling, etc)...

This is quite odd none-the-less...

Keep the thread updated if you will, I'm interested in getting a better understanding in general, and of course helping out where I can...

Diligence Rules the Day

Hang in there...

[Jondav1120]

Hi Mike,

Is the noise only in tracks that have been recorded through the D8B? If you were to play a clean track back from the HDR through the D8B and re-record on the HDR, does it then have the noise added to it?
I'd have a look at the +/-16V supplies, it could be noise on the regulated supplies.

Best regards

John

[Old School]

Hi All,
Good suggestions, all of them. Oh and by the way, I know how to describe the noise so that most will know what I'm talking about. If you remember what an Aphex Aural Exciter sounded like, that's the noise. First I did what Phil said, with my vocal mic trim set where it usually is for the average vocalist, I recorded just the room. Upon playback, I could hear nothing but silence, so I kept using the envelope tool to boost the volume 6 db at a time, render the file and repeat until I could hear some noise, this occurred at +42db. But it was broad spectrum noise, not just High Frequency. To prove this to myself I boosted 1 band of the parametric eq +12db and then I turned on the gate and turned up the sensitivity until the noise disappeared. Then I swept all the frequencies to see if some were still present, they were not. No matter what frequency I picked, the gate always came on at the same point, so I suspect that this noise is just the normal noise floor of the unit.
Next, acting on Dok's intuition that it might be thermal related, I opened an older session and checked out the vocals. The first vocal that was laid down was clean. The next (I know what was recorded first because when doing harmonies I always record the lead vocal, then the lower part and then the higher part) vocal had a slight noise and the last a little more, none of them as much as I have now but there none the less. So quite possibly something is getting hot somewhere in the input section of the console.
Next, following Jondav's advice, I opened an even older session and bounced a pristine vocal back through the board and recorded it to another track on the HDR. No noise.
What all this adds up to, I can't quite get my head around as to how to proceed from here. I'm not real keen on opening up the console and trying to solder new components (if I can find any and know which ones) to a PCB. I'm hoping somebody can come up with a plan for me, as buying a new console at this point in time would be difficult for me, but it's either fix it, buy new or go out of business.

Many thanks for your help and have a blessed day,
Mike

[Old School]

By the way, I'm not knocking the Aphex or anyone who uses one. I have heard it on many Top ten records from major labels. But my noise, while similar, does not track the vocal smoothly at all and jumps out at you abruptly instead of subtly.

Mike

[Jondav1120]

Hi Mike,

Next, following Jondav's advice, I opened an even older session and bounced a pristine vocal back through the board and recorded it to another track on the HDR. No noise.

Ok, I'm assuming that your audio path for this test is fully digital (i.e. ADAT or TDIF connections between the HDR and the D8B)?
If it is fully digital then I would think it's likely that the noise is being introduced through the analog circuitry in the desk. Do you have any way to record a track using an outboard preamp that can connect to the D8B digitally?

Another possibility...could it be the channel filters? Personally, I don't think it likely, but might be worth eliminating this as a possibility...

Best regards

John

[Old School]

Hi John,
Yes, you are correct, fully digital Adat connections. I always keep the channel filters off when recording or mixing. Per your suggestion, this afternoon I'm going to borrow an analog console and Install a dio-8 card in the HDR to see if I can record a vocal with no noise.

Thanks and have a blessed day,
Mike

[Jondav1120]

Hi Mike,

Sorry, should have explained myself better! I was wondering if you had some thing like an 8 channel pre amp to ADAT unit (similat to the Behringer ADA8000 or Presous Digimax D8) that you could send into one of the ADAT inputs on the D8B, patch that input out through to the HDR and record. If you can get a clean recording that way, I think the problem would then lie outside the digital section of the D8B.

Regards

John

[doktor1360]

I was wondering if you had some thing like an 8 channel pre amp to ADAT unit (similat to the Behringer ADA8000 or Presous Digimax D8) that you could send into one of the ADAT inputs on the D8B, patch that input out through to the HDR and record. If you can get a clean recording that way, I think the problem would then lie outside the digital section of the D8B.

This is an excellent triage execution point, sidestepping & effectively isolating the analog circuitry in D8B. Personally, Spidey Sense is beginning to tingle as I suspect that perhaps something discreet (coupling cap, resistor, or some other) could be involved... in the end, replacing the pc board involved and avoiding surface mount repair work would be ideal here should this be the case. The funky hi-end noise leads me to believe a rogue capacitor is involved here somewhere, but this is all speculation at this juncture...

Really interested in the latest test result(s), and ultimately helping Mike out - as I'm sure anyone reading this thread are (hang in there!)...

Diligence will win out here...