Hi Pensadians, What a great community this is that we have here on FB – it is awesome to have so many people willing to give & share advice and learn from one another. My love of audio comes from a musical background as opposed to a technical one, but I am always learning, and that’s the key… Anyway, I have a technical question about system noise on my home rig on PC. I have all but gotten rid of the problem, which I’ve lived with for some time, and I think that I am as close as I am gonna get to solving it on my own. This is a call out for those of you who are technically minded and perhaps know a thing or two about power, PC electronics, cables, amplifiers and how they all interact. My problem: I have identified that switch mode noise is leaking into my speakers via the usb cable that services my Scarlett 6i6 interface. Regardless of whether I run Ableton Live or Pro Tools, the problem still exists. I have Yamaha HS-50M monitors, which take audio from the interface on balanced quarter inch jack cables, are bi-amped internally and running from their own power point separate from the PC. If I use my laptop on battery power, running the same 6i6 and speakers, the noise disappears. As soon as I plug in the laptop to any outlet, the noise returns as it does in the desktop PC setup. The same problem disappears on a friends’ Mac laptop plugged into the same house power outlet. I’m not willing to switch to Mac at this point in time and would rather try to solve the issue on the PC if possible. The Scarlett 6i6 is a self-powered interface via an AC adapter power pack. Where I plug this in has no bearing on the level of noise being transferred into the system. Removing the usb cable from the 6i6 when the speakers are on (but turned down) gets rid of the noise straight away – like a night and day difference. This led me to trying out various modified usb cables, such as those missing the grounding or power, as I figured that the interface already had its own power supply – separate from the PC – in contrast to my old M-Box 3rd Gen (which I blew up, lol) that only used the usb cable power. The M-Box 3rd had the same issue as the Scarlett 6i6. It was not until I cut the power wire on the usb cable to the 6i6, did I hear a difference, as the noise disappeared by about 98-100% depending on CPU load (a massive difference). I would have classed this as a successful solution, until I discovered a small problem… Unfortunately, despite Focusrite explaining that the 6i6 doesn’t require usb power, it seems that the PC does in order to identify the interface and communicate with it. And whilst it still passes clean audio, in the sense that it no longer has the noise issue, it stops or stammers its way through playback and is unusable. I may get a few seconds of clean audio, only to have the device cut out intermittently and then completely. I purchased a powered 3.0 usb hub, which I have plugged into a usb 3.0 port, with the [usb 2.0] Scarlett 6i6 running off of that. This has made little difference to the noise issue. I also tried running off of regular 2.0 ports. No differences. The switch mode noise itself is at a constant level and is irrespective of the volume on either the interface or the speakers themselves. I’ve tried adding resisters into the ground wire of the usb cable, as per some advice I received, but this resulted in the same sort of issues I described with regards to cutting the power and ground wires. I have very little money to throw at the problem and would appreciate any common sense solutions that I may have overlooked. Whilst the switch-mode noise itself doesn’t end up in my final mixes, it does make mixing a challenge. I have measured the noise at the speaker (on the tweeter) at around the 54dB mark and in the 1kHz range. (Listen to gained up audio recording of it - attached). I do have at my disposal: A soldering iron, solder, various cables, cable ends, some resisters, a multimeter (which I need to learn how to use) and an SPL meter. Any relevant advice welcomed. Thanks!
Posted on: Thu, 28 Aug 2014 02:39:55 +0000
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