Whatever happened to those weird noises affecting nearby speakers when we received a call on a cell phone back in the days, as illustrated in the link?



I was appreciating the nice little attention to that detail in gta4, but it got me wondering how come it’s gone nowadays.

In: Engineering

8 Answers

Anonymous 0 Comments

If I switch from wifi to mobile data, I won’t get the familiar “dun da da dun da da dun” noise, but I will get a steady ‘gggggggg’

Anonymous 0 Comments

This is pretty tough to ELI5, but I’mma take a shot:

Back when cell phones first went digital, there were two competing “languages” for the cell phones and towers to use. CDMA and GSM. When wireless things talk to each other digitally, usually only one can talk at a time, otherwise the other stuff gets confused as it can be hard to tell what parts of what it is hearing is from one thing versus another. CDMA uses a system where the wireless radios in the devices are pretty much always on. GSM used a system called TDMA which meant each device gets so much time to send a signal, then other devices get turns.

In GSM when it isn’t talking it turns off the transmitter on its radio. It then turns it back on when it talks. Have you ever played with a really old amplifier, like one from the 70’s or so? When you turn them on they can make a pop noise as the power is applied to the speakers. The GSM radio is making a pop noise every time it turns on.

The actual digital signal of the cell phone is so high pitched, that even if your speakers could play it, you wouldn’t hear it. But those pops are timed just right so that they add together to make some awful sounds to our ears. (Non-ELI5, the frequency band of the radio switching is in audible frequencies).

While those pops can be picked up in just about any electronics, on their own they are not strong enough to move a speaker, at least not enough to be heard by humans. However, when they get picked up by the electronics that are then amplified, you hear them over the speakers. This is even more likely to happen if there are microphones around, as microphones put out such a low level of power they get amplified twice. Once to a level that regular electronics can work with them (called Line level, usually done by a pre-amp), then again to be enough to move speakers.

Why don’t we hear it anymore? When GSM moved to 3G, it went to a “language” called UTMS. UTMS uses a new version of CDMA, which wasn’t compatible with the old version of CDMA, called WCDMA. CDMA providers still used regular CDMA for 3G. When all the providers started going to LTE, it was decided to use WCDMA for LTE.

There are other signals and things on cell phones that can cause noises in audio systems, but the very distinctive and memorable one was the GSM noise.

Note below:
US GSM providers: AT&T, T-Mobile (and all the companies that got bought up by them so that we really only have 4 providers today)
US CDMA providers: Verizon, Sprint (and all the companies that got bought up by them so that we really only have 4 providers today)

So if you were in an area with no AT&T or T-Mobile coverage you might not have ran across this.

Anonymous 0 Comments

Yea I remember dating my first gf and I’d leave my phone by the speaker so I could tell when she was about to text me. Good old days

Anonymous 0 Comments

Microphones do this that are not connected to speakers (monitored with headphones). Leads me to believe it’s the input device catching signals, not the output.

Source: I own a recording studio.

Anonymous 0 Comments

Commenting to follow, I have a Yamaha music keyboard that’s 9 years old that makes sounds if I get a call when it’s close. The speaker makes the sound before the ringtone even starts

Anonymous 0 Comments

The band of the radio spectrum in use might have changed as we switched from GPRS / 2G to 3G and onwards. Higher frequencies being needed to transmit more packets of information at a faster rate.

Anonymous 0 Comments

The cell phone transmits quite a bit of RF energy when it is talking to the tower. That energy can leak into the amplifiers in a stereo system and disturb their operation, creating the sound you hear.

I don’t know exactly what happened, but I would guess they fixed this issue by:

– shielding the stereo amplifiers better (metal box)

– adding RF filters to the amplifier inputs

– making opamps with better RF rejection (basically built-in filters)

Something like the above. I would also hazard a guess that there are probably a lot of stereos floating around where this still isn’t fixed.

Anonymous 0 Comments

Only 00’s bois will remember, or however kids are talking these days.