6 ms·

Everything discussed in the article is 4-pole, isn't it? L, R, G, Mic? These days, Apple devices are 8-pin 2-lane lightning, and use separate lanes for audio

by brians 10y ago

Everything discussed in the article is 4-pole, isn't it? L, R, G, Mic? These days, Apple devices are 8-pin 2-lane lightning, and use separate lanes for audio and control. The Apple EarPods appear to be 7-pole: separate grounds for each signal wire, all as twisted pair. That's pretty cool, as someone who wants earbuds to work well near RFI.

Godel_unicode 10y ago
> ...wants earbuds to work well near RFI. This is the first time I've heard that argument, what RFI are you near that was breaking normal headphones?
- kuschku 10y ago
  > what RFI are you near that was breaking normal headphones? Mobile phones. The good old br t br t brrr tt br whenever the mobile phone thinks it has low signal and fires at full power and causes interference. A video demonstrating it: https://www.youtube.com/watch?v=8TWXCVbBTcc https://www.youtube.com/watch?v=8TWXCVbBTcc
  - tjohns 10y ago
    That sound has less to do with power level, and more to do with what mode your phone's modem is using. Specifically, that sound is associated with TDMA-style networks (e.g. 2G GSM), since the transmitter has to rapidly switch on/off, giving other phones a chance to transmit. This induces a series of audible-frequency voltage spikes in nearby cables. CDMA-style networks (e.g. CdmaOne, 3G GSM, LTE) don't have that problem, since the transmitter is effectively always on while transmitting. That's why you don't notice that sound very often anymore.
    - yaantc 10y ago
      LTE uses OFDMA, which has nothing to do with CDMA (no superposition and coding separation). OFDMA is a combination of frequency and time division: time wise, the allocation unit is a subframe of 1 ms (to be compared with a 2G GSM burst duration of 0.577 ms, so not that far) and frequency wise a subframe is made of "resource blocks" (RBs) of 12 subcarriers of 15 kHz each (so 1 RB = 180 kHz total). What's allocated to a device is a set of RB in a subframe, and this is repeated as needed accross subframes in time. 3G used a 10 ms allocation unit, but with HSPA it's been reduced to 2 ms to become more "TDM-like" (it turns out that in real life code superposition is not so good, better split in time and do less superposition: less interference, less power consumption, better results). I honestly don't know the source of the 2G noise, but from the above it's not as simple as TDM vs. no TDM, as current 3G and LTE both in practice have a time-based allocation component on roughly similar granularity as 2G. One difference could be the transmission power: 2G can go up to 2W, while LTE is 200 mW maximum so 10 times less. I don't have 3G peak Tx power in mind, but in practice I guess it should be closer to LTE than 2G (interference minimization in a same frequency / reuse 1 network: both LTE and CDMA are reuse 1 deployment, while 2G is not). That will certainly cause a 2G device to have higher power spikes. And I guess the details of the transmit pattern are likely to play a role too.
    - kuschku 10y ago
      > That's why you don't notice that sound very often anymore. Except yesterday. And today. And every second day in my life. Because even my Nexus 5X in a 4G network occasionally sends/receives SMS in GSM mode.
      - lightedman 10y ago
        I hear it every day with my 4G Moxee X1 sitting next to my Technics stereo. Anyone downvoting you must not realize this sort of interference is UBIQUITOUS and can be triggered even by someone with loose spark plugs in their engine.
  - semi-extrinsic 10y ago
    Interesting; I essentially haven't heard that sound in a decade, but then it was ubiquitious. Have we gotten better at designing TVs/stereos/headphones to avoid this? Or have phones changed? Edit: thanks to sibling comment for explaining.
  - pmarreck 10y ago
    that's just a 2G idiosyncrasy and went away with 3g and later
    - kuschku 10y ago
      Considering I heard it yesterday, while my phone was in 4G mode, I’m pretty damn sure it’s still an issue.
PascLeRasc 10y ago
Ground is an "implied pole" as you'd need it for anything, it's just 3 different upstream channels (L,R,mic) feeding into it.

by brians 10y ago

Godel_unicode 10y ago

> ...wants earbuds to work well near RFI. This is the first time I've heard that argument, what RFI are you near that was breaking normal headphones?

kuschku 10y ago
> what RFI are you near that was breaking normal headphones? Mobile phones. The good old br t br t brrr tt br whenever the mobile phone thinks it has low signal and fires at full power and causes interference. A video demonstrating it: https://www.youtube.com/watch?v=8TWXCVbBTcc https://www.youtube.com/watch?v=8TWXCVbBTcc
- tjohns 10y ago
  That sound has less to do with power level, and more to do with what mode your phone's modem is using. Specifically, that sound is associated with TDMA-style networks (e.g. 2G GSM), since the transmitter has to rapidly switch on/off, giving other phones a chance to transmit. This induces a series of audible-frequency voltage spikes in nearby cables. CDMA-style networks (e.g. CdmaOne, 3G GSM, LTE) don't have that problem, since the transmitter is effectively always on while transmitting. That's why you don't notice that sound very often anymore.
  - yaantc 10y ago
    LTE uses OFDMA, which has nothing to do with CDMA (no superposition and coding separation). OFDMA is a combination of frequency and time division: time wise, the allocation unit is a subframe of 1 ms (to be compared with a 2G GSM burst duration of 0.577 ms, so not that far) and frequency wise a subframe is made of "resource blocks" (RBs) of 12 subcarriers of 15 kHz each (so 1 RB = 180 kHz total). What's allocated to a device is a set of RB in a subframe, and this is repeated as needed accross subframes in time. 3G used a 10 ms allocation unit, but with HSPA it's been reduced to 2 ms to become more "TDM-like" (it turns out that in real life code superposition is not so good, better split in time and do less superposition: less interference, less power consumption, better results). I honestly don't know the source of the 2G noise, but from the above it's not as simple as TDM vs. no TDM, as current 3G and LTE both in practice have a time-based allocation component on roughly similar granularity as 2G. One difference could be the transmission power: 2G can go up to 2W, while LTE is 200 mW maximum so 10 times less. I don't have 3G peak Tx power in mind, but in practice I guess it should be closer to LTE than 2G (interference minimization in a same frequency / reuse 1 network: both LTE and CDMA are reuse 1 deployment, while 2G is not). That will certainly cause a 2G device to have higher power spikes. And I guess the details of the transmit pattern are likely to play a role too.
  - kuschku 10y ago
    > That's why you don't notice that sound very often anymore. Except yesterday. And today. And every second day in my life. Because even my Nexus 5X in a 4G network occasionally sends/receives SMS in GSM mode.
    - lightedman 10y ago
      I hear it every day with my 4G Moxee X1 sitting next to my Technics stereo. Anyone downvoting you must not realize this sort of interference is UBIQUITOUS and can be triggered even by someone with loose spark plugs in their engine.
- semi-extrinsic 10y ago
  Interesting; I essentially haven't heard that sound in a decade, but then it was ubiquitious. Have we gotten better at designing TVs/stereos/headphones to avoid this? Or have phones changed? Edit: thanks to sibling comment for explaining.
- pmarreck 10y ago
  that's just a 2G idiosyncrasy and went away with 3g and later
  - kuschku 10y ago
    Considering I heard it yesterday, while my phone was in 4G mode, I’m pretty damn sure it’s still an issue.

PascLeRasc 10y ago

Ground is an "implied pole" as you'd need it for anything, it's just 3 different upstream channels (L,R,mic) feeding into it.