Many modern digital audio devices including but not limited to laptops, notebooks, tablets, sound cards, keyboards and etc. can produce audible humming noise when connected to the amplifier, mixer, or monitor speakers. This noise occurs when the signal source is powered with AC adapter plugged into the outlet. Why? To answer this question I would have to write another article, but the subject of this one is about how to eliminate this noise. Fortunately, this is a common issue and there is a number of solutions that can be approached from two different directions. First, to do something with the power and the second, is to do something with the audio signal path. Let’s look at each option in more details. You can also check out the video at the end of this article where we explain and show different options.
For example. If a notebook is connected to a speaker monitor, it probably will generate humming noise noise in the audio signal (otherwise you wouldn’t be reading this article). If power supply is disconnected, the noise disappears. So, looks like the problem is in the power. (if not, you are in trouble and should try using direct boxes, read further.).
The easiest way to get rid of humming noise coming from the laptop, notebook or any other sound source, is to use some kind of power filtering device. We tried few options, but the least expensive solution was the HumX adapter. It has a built-in power insulating transformer and it’s really easy to use. Just plug it into a power outlet and then plug the device (computer, laptop, soundcard etc) into it. Just make sure the total load does not exceed 6A or 720 Watt. So far this unit never failed us. We used it for laptops, external sound cards, keyboards and were always satisfied with the result.
Using direct boxes
This option is for more advanced audio users and usually used during live performances or recording sessions. They key is to use a direct box with ground lift option. There is number of direct boxes that we use at ergProductions, and even more options when it comes to a choice of direct boxes currently available on the market.. Some manufacturers make direct boxes specifically designed to accept signals from laptops, computers or other digital devices equipped with “mini jack” stereo output. Others designed to accept signals from instruments like bass, guitar and alike. Let’s look at one of them as an example.
Whirlwind pcDI. Although this direct box is a bit pricy, it is great for use with notebooks and laptops. It comes with different connector options. The direct box on the picture accepts minijack (3.5mm), rca or ¼inch jack and outputs the signal to two XLR outputs. It can also combine stereo signal into one mono output, work as signal splitter (dual mono) or pass through complete stereo signal. This makes it perfect for connecting consumer level devices to the mixing board or PA.This DI also allows to pick up the signal from very strong signal source (like speaker output of the guitar combo) without damaging the input on the receiving end of the signal path.
There is one limitation though. DI can be used in setups where sound amplification system equipped with microphone preamplifiers. So if you run straight into the power amplifier or DJ mixer with line level RCA or ¼ TRS, the signal coming from the DI will not be strong enough to drive you system to the full power. Therefore using the HumX would be a better option.
So, we discussed two ways how to eliminate humming/buzzing noise coming from laptop, computer, notebook, tablets or other sound sources. Which one to choose is entirely up to the user and depends on application. We use both options, since during live shows, it is almost impossible to guess what kind of equipment people will try to connect to our sound system. Also, watch the video below where we explain aforementioned techniques in studio environment.