Author Topic: Audio over HDMI  (Read 1470 times)

Seanhump

Audio over HDMI
« on: June 15, 2022, 02:57:27 pm »
Quick one...

(and long time no posts, but been reading frequently ...)

Is (or can it be) the audio output enabled over the HDMI socket ..

Just looking at possible ways of getting a cleaner output from the PAW unit - its quite noisy using the 3.5mm jack

Thanks

PS - great work on the iGrid stuff - its working like a charm ...
Pilotaware user ...

steveu

Re: Audio over HDMI
« Reply #1 on: June 16, 2022, 02:59:04 pm »
Quick one...

(and long time no posts, but been reading frequently ...)

Is (or can it be) the audio output enabled over the HDMI socket ..

Just looking at possible ways of getting a cleaner output from the PAW unit - its quite noisy using the 3.5mm jack

Thanks

PS - great work on the iGrid stuff - its working like a charm ...

This assumes that you'll have something HDMI compliant to extract the audio from the datastream?

Another possible way to get a decoupled output from the PAW is to use a Bluetooth to 3.5mm stereo jack converter.

Pair this with the PAW...

https://www.amazon.co.uk/Anker-Soundsync-Bluetooth-Connection-Headphones/dp/B07H5C2BQX/

But what exactly is the audio noise on the PAW?  Isn't it worth trying to trace this?

If it's mag/alternator noise, is the cap across the regulator dead or not installed?

Is the supply to the PAW the right 12V/USB adaptor?

exfirepro

Re: Audio over HDMI
« Reply #2 on: June 16, 2022, 04:20:15 pm »
Hi Sean,

Nice to hear from you again, I was beginning to think you had dropped off the planet :)

You still Flying helis?

Not aware if Lee ever configured PAW to output audio on the HDMI - I’m certainly not aware of anyone using it. Personally, I haven’t used Bluetooth either since the early testing as I haven’t got round to upgrading my helmet with a Bose headset yet, so I still run hard wired audio, - currently with an audio mixer to combine PAW and SkyDemon audio which are (both) then fed via my Flycom intercom. Works OK for me.

Your noise could be from the Pi processor - have you tried a Ground Loop Isolator in the audio line? Not the technically correct solution, but lots have achieved positive results with them. Certainly worth a try.

Oh, and you are right about iGRID - I have been testing it since late last year with extremely positive results.

Best Regards

Peter

p.s. Steve, Sean was one of our regular long-term testers back when we did the pre-Beta testing of Bluetooth with the early Rosetta’s. IIRC he managed to get it working with his Bose A20s in the Helis, but in those days the pairing wasn’t persistent, so had to be paired before each flight. (Still not sure if that has been addressed yet - Lee ?)
« Last Edit: June 16, 2022, 04:22:10 pm by exfirepro »

steveu

Re: Audio over HDMI
« Reply #3 on: June 16, 2022, 06:20:45 pm »
Your noise could be from the Pi processor - have you tried a Ground Loop Isolator in the audio line? Not the technically correct solution, but lots have achieved positive results with them. Certainly worth a try.

The problem with the passive version of these is that there is a massive drop in signal level... good if you have mixer with gain to boost back up to the right level, but if you are simply using it in line then it's problematic - it was deal breaker for the installs I tried it on. I made sure all power leads to PAW and intercom had ferrite beads on them.

p.s. Steve, Sean was one of our regular long-term testers back when we did the pre-Beta testing of Bluetooth with the early Rosetta’s. IIRC he managed to get it working with his Bose A20s in the Helis, but in those days the pairing wasn’t persistent, so had to be paired before each flight. (Still not sure if that has been addressed yet - Lee ?)

I know we managed to get it to work between a Microavionics intercom and the PAW, but I think it was then converted to 3.5mm jack at both ends as the pilot wanted to use the BT into the Microavionics for his phone... I think it was persistent, but not sure...

exfirepro

Re: Audio over HDMI
« Reply #4 on: June 17, 2022, 01:50:22 pm »
The problem with the passive version of these [Ground Loop Isolators] is that there is a massive drop in signal level... good if you have mixer with gain to boost back up to the right level, but if you are simply using it in line then it's problematic - it was deal breaker for the installs I tried it on. I made sure all power leads to PAW and intercom had ferrite beads on them.

Yes, Steve, I agree, it’s always best to look for the actual reason for interference and deal with it appropriately - often as you say by fitting ferrites to power and other signal cables, or simply re-making a dodgy connection or replacing a potentially high-resistance earth.

I have, however, come across a couple of cases where the interference to audio was clearly coming from the Raspberry Pi in the PilotAware - and was being output to the intercom via the audio jack. In both cases, ferrites on the audio lead were of no help whatsoever, but fitting Ground Loop Isolators was effective, and probably the only solution (short of replacing the Raspberry Pi).

As you say, not always the best solution, but can certainly worth trying.

Best Regards

Peter

steveu

Re: Audio over HDMI
« Reply #5 on: June 17, 2022, 02:05:59 pm »

I have, however, come across a couple of cases where the interference to audio was clearly coming from the Raspberry Pi in the PilotAware - and was being output to the intercom via the audio jack. In both cases, ferrites on the audio lead were of no help whatsoever, but fitting Ground Loop Isolators was effective, and probably the only solution (short of replacing the Raspberry Pi)

I wouldn't put ferrite beads on audio leads, I'd put them on power...

If ground loop isolators are effective, then I think there's an earthing problem... it's worse on 3.5mm audio because it's an unbalanced signal. Had it been balanced audio on XLR, the problem wouldn't have arisen 90% of the time.

Seanhump

Re: Audio over HDMI
« Reply #6 on: June 17, 2022, 03:44:25 pm »
Hi Peter

It's been very busy for quite a while, and whilst I've been lurking, I've not been actively posting, but I still use (and promote) the PAAW on a daily basis ...

The noise in question is from the Pi by the looks of things, and I do have a suitable adapter to get analog audio from the HDMI output ..

Setup is as follows ... (its in a Turbine Heil, so no Mags or alternator, just the generator ...)

12v outlet to a Anker USB power strip. Juice Bitz 50cm cable (correct gauge) to the PAW, with ferrite ring.

Nothing else hooked into the other 4 USB outputs on the Anker ..

Good quality 3.5mm cable (with ferrite) to Bose A20's - its a semi permanent install, and I use Bluetooth on the other portable unit I have.

The noise *sounds* Pi related and doesn't follow any changes to engine speed or generator output - its persistent with a battery pack too ...

I've ordered a ground loop isolator and will try, but figured the HDMI output would be a neater solution if the audio was / could be (its a config change) piped to it ...

I'm in the offending aircraft tomorrow and will try the isolator and report back RE the levels - I do have a little 12v audio mixer that could also be tried

Cheers
Sean
Pilotaware user ...

Seanhump

Re: Audio over HDMI
« Reply #7 on: June 18, 2022, 10:48:47 pm »
The Ground Loop isolator arrived, and has quietened the noise right down - the downside is that it's attenuated the signal some - it's not too quiet, but it could be a little louder

If there's anything from Lee on the HDMI output then that may help with a cleaner signal ..!

Ideally I'd not like to add an mixer as it's one extra thing to add to the mix of bits!!
Pilotaware user ...

Admin

Re: Audio over HDMI
« Reply #8 on: June 19, 2022, 07:43:59 am »
Hi Sean
I haven’t had any other requests for hdmi sound output
I guess it is technically feasible, but what would it be used to drive ?
What equipment do you intend to connect?
Thx
Lee

Seanhump

Re: Audio over HDMI
« Reply #9 on: June 20, 2022, 07:03:49 pm »
Thanks Lee

I've got a HDMI -> VGA/3.5mm audio dongle so I can pick up the audio from there - hopefully with a cleaner signal, and there into the headset or intercom

In theory, its just a line or two in rasp-config (a super-nice to have would be a tick box on the PAW config page ..!!)

Cheers
Sean
Pilotaware user ...

steveu

Re: Audio over HDMI
« Reply #10 on: June 20, 2022, 07:23:23 pm »
In theory, its just a line or two in rasp-config (a super-nice to have would be a tick box on the PAW config page ..!!)

Do you think it might be free from the low gain restriction of the 3.5mm jack?

I've seen a couple of dedicated HDMI to audio boxes with the option of gain adjustment, which I need to investigate but it looks like gain adjustment as opposed to signal attenuation...