this post was submitted on 16 Mar 2024
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Induction would happen.
Older PCS cellphones operated on a frequency and power level that if the phone was placed near enough to an analog audio connection, typically for speakers, somewhere before amplification happened, and the audio line was not shielded, it would induce enough current in the line to come through the speakers as a repetitive set of tones.
Usually, this was a precursor to a data transfer, either to initiate a call or transfer a text message.
This was eliminated with two main things. First, cellphone frequencies and power levels have been optimized a lot, also the frequencies used for most cellular communication have changed. All these changes may mitigate the effect. The second thing is that nearly no unemployed analog audio is moved over distance. Most devices use either digital signalling or similar for all their communication. Bluetooth audio devices are notable here. Bluetooth headphones, "true wireless" earbuds (airpod style), and Bluetooth speakers, make up the majority of consumer audio. For wired audio, it's usually usb, which uses digital signalling all the way into the device, where the DAC/amp is directly wired together and then pushed to the speaker drivers, whether those are for loud speakers or headphones. The last bastion of analog was headphones, and since headphone jacks are out of fashion on cellphones, almost everything uses digital audio transmission.
Even for TVs and such, HDMI uses digital signalling for audio. Analog audio is basically non-existent for anything outside of home theatre applications, where the analog signals are entirely post amplifier, out to speakers....
Even if cellphones would induce noise on analog lines in the same way they used to, there's no analog lines for the signal to be induced onto that would create a noise in the same way.
I only know all this because I work in tech with a specialty in wireless, and I hold an amateur radio operator license, which requires that you know about these things, and I've self studied electrical and magnetic interactions as an extension of all the EM transmission knowledge that I needed to have. The physics are quite straight forward to at least grasp a basic understanding of the mechanism. By no means do I consider myself an expert, physicist, nor scientist. I just know enough to understand.
๐ I feel so old rn. all my computers and TVs have 3.5mm analog connected to a set of separate speakers. I use 2 pair of 3.5mm-connecting headphones every day (work, home). I'm nowhere near an audiophile or anything... none of it is even approaching high-end. I didn't know people had abandoned non-bluetooth so much. guests always compliment how amazing my TV sounds though...
I'm with you, but I started to make inroads into digital pretty early on, around when home theatre surround sound became a thing. I got a JVC 5.1 home theatre audio system, and picked up an add-on for my sound blaster which added optical output, and plugged that into my JVC, so I could get 5.1 surround while watching DVDs on my 25" CRT.... I think it was 25? 1600x1200. I remember that much about it.
I still have, and use, my JVC. On my PC, I've gone a bit more audiophile than what most people do. My desktop system doesn't have any audio on board, so I picked up a Yamaha USB mixer. It acts as an audio interface (headphone out/mic in) for my system, and I use analog wired headphones for it.
My cellphone doesn't have a headphone jack anymore, and neither did the last one. So it's been about 6 years since I had a headphone jack on my phone. When I first got a phone without a headphone jack, I found a Bluetooth device that's essentially just a headphone jack. The one I have is "premium" and not the cheapest, it's a Fiio BTR5. I have a small set of headphones for use at home and on the go. For home I'm mainly using a pair of Sennheiser HD 598, which I've had for years, and on the go, I use mainly IEM style earbuds, usually moondrop starfield, but I have a couple other pairs. I still have my old speakers and sub that I used on my PC for a while, but I don't have them set up. They don't sound very good, and my headphones are comfortable enough that I prefer them anyways. When I'm on my computer, I usually don't want to broadcast the sounds from my games and such to anyone else, and the Mrs works afternoons, so I would disturb her if I used them often.
The JVC is now being used for my TV, still over an optical connection from my TV. It still sounds great and I'm still using the original speakers for them.
I like telling anyone who will listen about my Fiio, since, even if they don't buy one because of the cost, there's inexpensive alternatives, even some from Fiio like the BTR3, which will help beloved headphones out of the landfills, and keep people from buying Bluetooth devices that are going to fail within a few years. I've had my Fiio for 5+ years and I'm always looking for reasons to use it. The nice thing about it is that it can operate in USB mode (no Bluetooth) and it can also charge while it's being used. That's more than I can say for almost all Bluetooth headphones on the market, especially the airpod style ones, which need to be returned to their carrying case to charge. Other Bluetooth headphones generally turn off when you plug them in to charge, even if the charging port is able to be connected while you're wearing them. Some newer units can do this, but it's still fairly rare. So I use my Fiio with my phone on the go, with my PC at home and at work when I want to listen to music.... It's pretty handy. No USB drivers are needed, so just plug it in and use it in USB mode, which makes my boss and IT guy happy, since I don't need to be an admin to get it working.
Anyways, enough from me. I just wanted to share my experience and thoughts on it. Hopefully this gives you (and others) some options when the wireless revolution forces you to seek alternatives.
I remember they came out with light up stickers or "charms" (a little dangly thing to hang off your phone) that used this effect and would flash RGB instead of (well, as well as) make that noise before a call came in. Those were simpler times XD
For my desktop, I have a monitor with built-in speakers and the audio is carried by HDMI - but its speakers are such junk that I have powered speakers connected to it via a headphone cable. I haven't noticed any weird noises before texts or phone calls, but I do get a faint buzz that changes with the contents of my screen... Oddly enough, bright white makes most noise, dark is quiet. That would make sense for analog video, but for HDMI it baffles me.
It makes sense, the DAC is in the monitor, but the monitor is an electrically noisy place, so the IC that's responsible for the DAC/AMP is picking up noise from the power circuitry in the monitor. It's common with cheap DAC/AMP chips, like what they use in low end motherboards and monitors.
Basically as power usage is increased the noise should be greater. Unfortunately it's a design flaw, so your only real option is to replace it to resolve the problem. You may see improvement with a ferrule, or you could try doing some hardware hacking and adding shielding around the audio circuitry.
The ferrule is the easiest and cheapest, but it may not fully resolve the issue.
Oh no, I get why the interference happens, it's more the content of the interference that surprises me. With analog video, a white screen is basically a 15 kHZ full amplitude square wave, but HDMI is encoded so regardless of the balance of 0s and 1s in the original content, the data stream should be just noise either way.
You mentioned powered speakers plugged into it, which means the output from the display is unamplified, and it is amplified by the speakers. So the wiring from the DAC, decoding the HDMI signal to the jack where the speaker is connected is analog and surrounded by very noisy digital circuits, especially power circuits, which induces the noise.
Most digital speaker systems, such as Bluetooth headphones have a single IC for both DAC and amp which effectively eliminates any induction of noise.
The weakest point in the audio system is the unamplified analog signal. Any induced noise is amplified with the intended signal.
The frequency heard is going to be a function of what signal is causing the induced noise. Depending on the display, it could be any number of subsystems. Usually related to the backlight, but not always. The noise is very likely completely unrelated to the audio being played.