Dell Computer Generates Recording Hiss

I recently setup a 2nd DAW workstation based around a Small Form Factor (SFF) Dell 7010; it is a 2014 computer, has Intel i5 CPU, 8G of RAM, 250G SSD (no mechanical hard drives) and the original 240watt power supply. I am now recording electric guitar using a Scarlett 2i2 as the interface with identical 6’ XLR cables and Shure SM57 microphones. I friend listened to my recordings and could hear a faint overtone, he called it a hum and he thought 120hz. I have done extensive isolation tests to see if it is 60hz and/or 120hz mains hum because of ground loops. It is not.

The simplest test I did was to remove all inputs into the Scarlett interface, crank the inputs of the Scarlett up to 10 and Audacity input at 10 just to see what the background humm or hiss or buzz level is. Using the Audacity Spectrum Analyzer shows a uniform noise from 30hz to 20k hz with a sharp drop off above. This is to be expected as the Scarlett has a very low noise floor but even the best interfaces turned up to max with the DAW software at max will record hiss, the latent noise of the interface. To confirm, there are no mics and cables plugged in.

Now the difficult part. I compared the background noise manifest as hiss level to a 2nd homebuilt computer I have. This other computer is in a mid size case, same i5 intel, two Western Digital raid arranged hard drives (no SSD) and a 430 W Corsair power supply (fairly new on the PS; I replace every 3 years). This mid-size computer is plugged into an APC brand uninterruptible power supply (UPS). Doing the identical test with the Scarlett, maxed out into maxed out Audacity in this mid-size computer, reveals 24db less hum. In other words the Dell is somehow creating 24 db more background noise. As a final test I moved the Dell and plugged it into the same APC UPS outlet so everything is equal. The Dell still produces 24db more background hiss.

Thank you for reading this far. I have also done tests with mic cables plugged in with dummy loads and cable and mics plugged in. With dummy loads the noise difference is still minimally 24db noisier with the Dell. With mic plugged in there is much lower frequency background noise in the 200h to 354hz range that is evidently louder than the 30h-20k hz hiss. The Dell with mics plugged in becomes 30db noisier if the inputs of the Scarlett 2i2 are turned to normal condenser mic input levels.

I called Scarlett and the tech has heard of this problem before; our discussion lead to it likely being the power supply in the Dell. As the memory is SSD, I can’t imagine it generating noise. Perhaps the cabinet and/or CPU fans? New Power supplies for the Dell are still available but perhaps I should just get another computer? I called Dell; they were not helpful.

Help!

Hi rschiller

Mains hum is about 50 hz (240 volt) in the UK.

Also you could have a bad earth somewhere in the chain

I found that keeping mains cables and audio cables completely separate goes a long way to keeping signals tidy. One very cheep and cheerful ways is to put audio cables inside tubular polystyrene pipe lagging. These offer a great deal of protection from being trodden on, and keep things tidy. They come pre-cut down their length.

Found this out in about 1976.

Have you tried rolling-off a few db at about 40hz, this should also effect 50hz frequencies.

Another way is to blot over mains hum by boosting the kick drum at about 60hz - this gives a nice thud. Adding a 200hz boost on the pedal click.

Most things like mains hum, get lost in the mix.

Don’t let it distract and stifle your creativity.

If you listen to many recordings there is a lot of dirt there, but is only noticeable if you whack up the volume on your amp full bore, turn the treble up and put your ear to the tweeter on the loudspeaker.

Post a clip here of your guitar without any effects or EQ, just the raw take.

Thanks for your response. It is not cable routing and/or mains humm because the problem occurs even with no input and with the computer plugged into an UPS which converts the wall AC to DC and back to AC. The UPS acts in this fashion identically to a 1:1 isolation transformer entirely eliminating any mains hum issues. I’m only recording solo guitar and have attached one, an arrangement of “Sleepwalk” Its is an exerpt and lowered quality because of this board’s files size limitations. The track is as recorded with no post production. You most likely will not hear the issue I described in my initial post.

Cheers!

Hi rschiller

Sleep walk - wow! Lovely recording - when I was a lad, my older brother gave me the original single by Santo and Johnny, anyway, I digress.

The only thing I can suggest is, unplug everything in the chain.

Start Audacity recording, and plug things again component by component, analyse the recording of each as you progress.

Have found this to be a slow, but methodical way of finding the culprit.

Glad you liked Sleepwalk. As you’re across The Pond I’m attaching my arrangment of Albatross by the late great Peter Green. In mono and lofi because of file size. If not clear in my initial post, I have done extensive tests with each piece of the chain added back in. I even tested just the cables both without mics and with dummy 100ohm loads.

signing off, Rick

I think you missed the obvious step. Stop recording on the computer.

The 2i2 gets its operating voltages from the USB system and is a complete slave to how “clean” that five volts is. There is a known problem where the computer and the sound adapter both depend on each other to clean things up. If neither does, you can get “frying mosquitoes” noise.

https://www.kozco.com/tech/audacity/clips/USBMicrophoneWhineClip.mp3

It got so common with home computers that Audacity has a filter designed for it.

If you’re using an adapter to USB-C, then you’re also having to deal with the USB negotiation for higher voltages and charging services. It’s not simple 5 volts any more. Yes, the data going from the 2i2 to the computer is digital and much less likely to create noise errors, but the DC supply is pure analog. It’s expensive to filter and condition, so nobody does.

Noise in computer systems can leap out of nowhere. I recently did a test recording where I got a Beyer dynamic microphone close to an iPhone and could hear the screen housekeeping whining and thumping at me. All the radio services turned off.

Also some basic electronics. The microphone system on a 2i2 is balanced, but the guitar/instrument connection is not. That means the body of the guitar is connected to the case of the 2i2, the case of the computer, the safety ground, and that clothes washer you have running in the garage.

Home computers only provide minimal filtering, conditioning, and shielding because who’s going to notice if your USB mouse or keyboard skips a beat every hour? Spreadsheets don’t have noise problems. I can account for the newer computer being noisy, too. They got really good at cutting corners.

Also, I think you covered this in the post, just disconnecting the 2i2 inputs is not a valid noise test. That turns the open connections into little antennas, ready and willing to pick up any electrical trash in the air. I woudnt be surprised if the noise comes and goes by just putting your hands close to the connections with the volumes all the way up.

Doesn’t have to be Radio Frequency, either. LED lighting is better at it, but earlier CFL lighting was famous for radiating at multiples of your power frequency. Even dimmed tungsten-incandescent can sing at you.

That’s an H4 sound recorder. It doesn’t have any of these problems short of environment and room noise.

It has XLR connections in the bottom. Newer recorders are much better at live recording.

I think that’s an H6 in the middle.

https://www.youtube.com/watch?v=MeCu3pm8IxE

Koz

Hi Rick

Love Albatross - lovely recording.

Hope you don’t mind, (please don’t shout) I put some double tracking on it, and rolled-off a bit of low end.

I used the duplicate facility EDIT - DUPLICATE and the TIME SHIFT TOOL to advance the duplicate by 40 milliseconds (i think they are milliseconds).

As for the gremlins in the machine - I wouldn’t worry. Judging by your mp3 sample they are little more than creases and can be ironed-out post production.

The fundamental concept of using a DAW allows one to use microphones and placements of choice. If the H4 allows stereo mic inputs and the digital engine produces same quality as Audacity, Protools, et al then that may be an option. However, you are rightly pointing to the 5v dc bus voltage as an issue and that voltage is produced (as all computer voltages are) by the single computer power supply. If you read some of my previous replies, I have isolated both computers from wall AC voltage by the use of an UPS which converts AC to DC and back to AC.

Isaac, Thank you for making me aware of your clever double track time shift idea! I would prefer a bit less shift however, I think this is a useful tool and a touch different than audacity’s echo effect.

thx!

Hi Koz, What is the name of the filter in Audacity and/or is it located in effects?

thx! Rick

What is the name of the filter in Audacity and/or is it located in effects?



Mosquito-Killer4.ny (363 Bytes)

Or you can get it from the site/archives.

This sound error (formerly known as “Yeti Curse”) produces tones in multiples of the USB data rate. The tool selects how many mosquitoes (harmonics) to filter out. 8 is usually enough. If you need more than that, forget the filter, change the computer.

There is a caution. The tool is sucking out musical tones right down the middle of the desirable voice frequency range, so it’s not “free.” It is creating some sound damage, but version 4 of the plugin is pretty good about not creating additional problems.


The Blue Yeti, an insanely popular microphone, got tarred with that label because it doesn’t have any battery processing. It uses the raw USB voltage to run the electronics and sensor. So every sloppy computer on the planet suddenly appeared with what looked like “Yeti” problems.

Wrong place and time.

tones in multiples of the USB data rate.

The standard data rate. If you’re USB doesn’t use the standard protocols, this isn’t going to work. Jury’s out on USB-C.

Koz

Koz, great and thanks. No free lunches in the audio world, eh?

Rick

No free lunches in the audio world, eh?

If you ask the home microphone makers, just buy their microphone, set up on the kitchen table, announce audiobooks, make a fortune, and retire to a nice cottage up the California coast.

It’s in a tsunami zone, near an earthquake fault, and it’s a time-share. But still.

Koz