It’s not to big for you or in other words. For you it’s ok.
Under what circumstances would one post someone else’s opinion without any context? I goes without saying that one’s own post containing a subjective observation is their own opinion.
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No, it is not too big. Do not wear slim pant :))
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Don’t know if this discussion has been continued in this thread or anywhere else in the forum more in-depth, but if anybody knows where, I would like to know.
My understanding: I2C is out for audio because it’s way too slow. I3C might work in theory but there are all sorts of caveats. The protocol is not made for audio at all. There is a protocol called I2S (which the phone doesn’t have enough pins for and can’t use) that is made specifically for audio. It is often used used together with I2C/I3C (these are for control signals like play/pause).
To get good audio through I3C, you would have to replicate the timing functionality inherent in and necessary for audio protocols like I2S with an oscillator, keep that strictly in sync with the system clock of the phone, marry that timing signal with the incoming I3C stream from the phone in a relatively powerful microcontroller, hand it (probably as I2S) to a DAC in which you could then plug your headphones. However, a “little” more work needs to be done before plugging the phones in does anything: You would have to implement an audio driver or even kernel module that translates “regular” system audio into I3C. I don’t think such a thing exists, so happy implementing. 
–> This does not seem like a sensible architecture and I don’t see a a realistic way to make the pogo pin infrastructure work for a 3.5mm jack TOH. Happy to be proven wrong though
If the pogo pins gave us USB, it would be much, much easier.
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As I very rarely use headphones with my smartphone, a small Bluetooth receiver powered by batteries (not rechargeable) would be enough for me.
Unfortunately, all Bluetooth receivers (with an AUX output) have rechargeable batteries. But for many users here, such this device would be the ideal solution if they use headphones more often than I do.
Why would you need an external bluetooth receiver, when the phone itself already has a bluetooth modem?
Sorry but in the past there was an article explaining why it’s impossible to properly hold and use a phone that’s bigger than 5”.
Holding it is far from the only factor I would consider when thinking about phone size. I want a screen that can fit a decent amount of text at a reasonable font size, that to me is more important than being able to reach every corner of the screen with one hand. I think the JP26 is pretty much the perfect size for me.
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…you need it to play music from your mobile phone through analogue headphones, which you plug into the AUX output of the Bluetooth receiver…
It is a little nonsense if you can use usb-c DAC to Jack 
using BT and then build-in dac in receiver consume more energy in total than just single DAC on usb…
I have a USB-C to AUX adapter myself (without a DAC) that works brilliantly with my analogue headphones (without any compression loss). However, as I have a magnetic charging socket plugged into my USB-C port on the J2, I don’t want to unplug it whenever I want to listen to something through my headphones.
And the power consumption of such Bluetooth receivers can’t be that bad, as they’re available in countless different models and sell very well.
- there is always some DAC (digital to analog converter) unless you listening old tapes or vinyls on analog devices
- if you compare absolutely same headphones it will cost you more power over BT because you have to encode audio for BT protocol, transmit, decode BT protocol in headphones …
- if you need charge while listening music get USB DAC with charger port
- if you use wireless charging you loosing about 10-20% of power, poor alignment may loss up to 70%, small devices has efficiency about 50% because of small coil. so wireless charging should be restricted especially in EU what trying to be green world saver with their unified connectors and so…
OK, if only the digital ‘audio’ signal is ever present on the USB-C port, then my ISY IKA-1000 must indeed have a DAC. Otherwise, it wouldn’t work. However, this is not mentioned anywhere in the description or technical specifications.
PS: I don’t charge wirelessly; instead, I keep a magnetic adapter plugged into my USB-C port at all times to prevent it from being damaged (over its lifetime) by the constant plugging and unplugging of the charging cable.
Ah, you mentioned a bluetooth receiver with an AUX output, so I assumed you’d connect that to the phone and would stream audio to it. I guess you mean the other way around?
You don’t generally output audio to the phone of course, I may need some more coffee.
Yes, something like the ‘LOGITECH Bluetooth Audio Adapter’, but designed for mobile use, and it should work with the J2.
My magnetic adaptors can transfer data ( Amazon.co.uk ). So I’d also need a USB-A (female) to 3.5 AUX (with DAC) adaptor to use my charging/data cable.
And does something like that actually exist?
Regarding your follow-up comment: I want the small magnetic charging/data adaptor to stay plugged into my USB-C port at all times. I do have a USB-C to Aux cable (with DAC). To use that, I’d have to remove my magnetic adapter – which I don’t want to do.
There are even (from two companies) magnetic adapters for the Aux socket. However, these are from different companies to my magnetic charging/data adaptor. It’s highly unlikely that it will fit.
That sounds like an interesting exercise, but why on earth would you bother with the phone’s system clock?
You get samples over I3C, buffer some amount of them, and hand them over to the DAC at the correct sample rate. Your microcontroller needs an oscillator anyway and normally I’d pick a frequency that is a multiple of what the DAC needs. Then you can just use one of the controller’s counters to derive that clock.
Yes, you would need that and it would make most sense for it to be provided by the base system. I haven’t studied the data sheet for the SoC. How are its audio peripherals handled - are they perhaps already connected over I3C?
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Right, a buffer underrun would result in clicks or other artifacts, which will be an issue with live audio. There should be a way to sync sample clocks. (Playback might be less sensitive, as you could request more samples from the file a bit “early”. Most people would not detect the pitch change if the DAC clock runs at 44.2 kHz instead of 44.1, and crystal oscillators normally have much smaller deviation.)
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Hmm, yes, but the jitter introduced by an asynchronous data delivery should be absorbed by buffering. I believe clocking out samples to the DAC (using crystal controlled oscillator) shouldn’t introduce any noticable jitter.
I’m assuming that any USB DAC would face the same problems with asynchronous data delivery, and the same countermeasures would apply.
I think professional audio hardware needs to deal with higher requirements than can be expected of a phone, e.g. including minimal buffering to keep sound from speakers close to direct sound propagation.
My 44.2 kHz vs. 44.1 kHz example (a 100 Hz sample rate deviation) gives a constant pitch change roughly equal to a 1/30 of a semitone, and a good crystal oscillator performs better than that.
I still doubt people would detect such a small pitch change while just listening to music. (A varying pitch would be much easier to detect, though, and simultaneously listening to a pitch fork and the recording of it would immediately tell the difference, of course.)
You are probably right .
I’m in the “3.5 mm camp” because I have good headphones I’d like to keep using until they break beyond repair, and I would prefer a TOH over a dongle to reduce wear on my single, precious USB connector.
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I won’t be the person implementing this and it is clear that some level of support from Jolla will be needed, so for me I think it’s a case of “hope for the best and prepare for the worst” (i.e. buying a USB dongle).
I know that feeling. I once suggested we’d connect headphones from above in a studio. We were constantly breaking the 1/4" plugs and someone had to solder on new ones. But I was laughed out of the room since that would “look ridiculous” Bluetooth would have been a good solution, had it existed.
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