Audio Testing

[brinzlee]

AllanBirt I think there may be an issue with the rPi socket.....there is a possibility you are not connecting the ground pin in the rPi audio out properly and its using the video as a ground which would lead to all sorts of problems like you are describing.
I purchased a stereo to stereo lead 3.5mm to 3.5mm jack, cut one of the plugs off then bought a 4 pin 3.5mm plug from CPC and soldered the braid to pin 3 and then the other two wires to pins 2 and 1 respectively. That way it keeps the stereo separation in the Bose.

AlanG glad you managed to get a bluetooth adapter so quick.....it's a neat little solution and one more wire less, to tangle!!

[brinzlee]

It depends what bluetooth adapter you are using.....mine is v4.0 and doesn't suffer any clipping at all

[AlanG]

Hi Ian

The Blackstar Tone Link bluetooth receiver http://www.gear4music.com/Guitar-and-Bass/Blackstar-TONELINK-Bluetooth-Audio-Receiver/1EOD that I use to get the audio from my tablet to my intercom did suffer from clipping originally but working with Rob Weijers (PocketFMS software guru for EasyVFR) he introduced a small wake-up tone in front of all the alerts which overcame this.  Strangely enough, using Brinzlee's Tx/Rx device as Tx from the PAW and receiving directly to the Tone Link attached to headphones there appears to be no clipping.  There is a very faint hiss behind the speech but not enough to be irritating.  So far so good, still to be tested live in the aircraft .  I'll let you know how it goes probably next week now.

Alan

[Ian Melville]

Thanks guys, I am using audio direct by cable from PAW. At the moment, and have SkyDemon anyway. No noise issues as I run off battery packs.

[AllanBirt]

Ok

I have modified my cable to a 4 pole socket and wired as per Raspberry Pi layout, this plugs into the PAW and on the other end I have the standard 3 pole socket, which then plugs into my Bose headset. Guess what..... still get the hiss !!!!

After looking though the raspberry forums this is a common problem, it seem you can still use a standard 3 pole sockets for audio only, if video is required than a 4 pole socket is required.

I have also copied one of the post below, regards to eliminating the hiss

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1. Add disable_audio_dither=1 to /boot/config.txt
2. Use an amplifier. The output is not meant to drive headphones directly.
3. Pick up a $7 USB audio adapter.
4. Pick up a $15 HDMI sound extractor.

The RPI was not sold as a high-fidelity audio device. These solutions will help. Try your HDMI extractor and please let us know how that worked for you!
--------

Out of interest has the: disable_audio_dither=1 been added to the PAW boot config file.

Maybe this is worth a try, I have not tried a ground loop isolator yet as still waiting for it to be delivered.

Not sure if I mentioned this but I even get this hiss from a brand new Raspberry Pi 2 v1.2, nothing installed, just powered straight from the box..... would this have a boot file from standard !!!

Kind regards

Allan

[brinzlee]

This really is strange.....have you plugged any other audio source into the Bose A20.....try using the same lead to say your iphone and play an audio file.....have you paired the bose to sky demon for audio alerts do you get any distortion with that ?

[AlanG]

Hi Allan

Can I ask if this hiss is there all the time the units are connected or only when speech comes through.
As I mentioned above I can hear a very faint hiss when an alert is transmitted.  It is not detracting from the speech, it is only really apparent as the speech stops, there is possibly a half to one second of hiss as the alert message ends then it is silent.
This is running the PAW in the house from a battery using the Bluetooth devices (as above post) into a pair of bog standard stereo headphones. 

Alan

[AllanBirt]

This really is strange.....have you plugged any other audio source into the Bose A20.....try using the same lead to say your iphone and play an audio file.....have you paired the bose to sky demon for audio alerts do you get any distortion with that ?

While at the airfield today tried my iPhone using the same cable and all was ok, but if I plug into the same USB socket as the PAW to power my mobile I get this interference noise.

I'll have to have a look at this Anker USB socket as it must be this causing this problem, I wouldn't expect this as this is no cheap unit.

I don't get any other interference when 2 devices are being powered by this, i.e. iPad & PAW, no noise via the radio which I would expect if there are earthing issues.

Another job for tomorrow.

I was also told to remove the earth connection within the AUX cable which connects both together and this made no change

[AllanBirt]

have you paired the bose to sky demon for audio alerts do you get any distortion with that ?

Morning,

Are you able to tell me what type of alerts will come from SkyDemon, would this be similar to the PAW, if this is the case I may use this method for getting traffic announcements 

Allan

[brinzlee]

No they are different....SkyDemon are alerting tones for airspace restrictions, terrain etc....whereas PilotAware is recorded voice announcements for traffic....

[AllanBirt]

Well after a day of taking my plane apart I believe I may have found the culprit which is causing the ground loop.

The problem is actually the earth on my Trig TY91 radio, if removed the problem goes away. Now what I've done was test all the earthing points on the 25 pin socket that connects directly to Trig radio only to find out that pin 22 has been joined with 9 & 19. Now I don't know if this is actually causing the problem as I'm unable to unsolder pin 22 as this has been all wired together with wire and then soldered too.

This was all done by Airworld UK when I purchased my Trig setup, I'm hoping that a fellow pilot may have the same setup as me with this pin not being wired to pins 9 & 19.



What I will do is speak to Trig tomorrow to see if this would actually will cause this interference !!!

With this connected I don't have any other issue, with internal intercom, talking to the ATC, no interference at all, that's until I hard wire my PAW using the AUX cable to my Bose headset.

I have tested my mobile using the same power supply as my iPad and created a Bluetooth connection to my Bose headset and all is ok, so it looks like my only option is to purchase a Bluetooth transmitter as recommended by Brinzlee.

I'm also waiting on delivery of my ground loop isolator, maybe this would resolve this too.

I am really annoyed if pin 22 is the culprit as I paid good money to have this wiring loom made up :-( :-(

Well tomorrow after work I'll have to put half my plane back together ;-);-)

[exfirepro]

Allan,

Looking at that diagram, it certainly looks like there should be no direct connection between the system ground (pins 9 & 19) and pin 22. Definitely worth a call to Trig. They are generally very helpful. Any problems let me know as I have contacts locally (they are just down the road from me).

Regards

Peter

[brinzlee]

I concur with Peter.....there should be no connection between those pins.....Sounds like a mistake on install

[AllanBirt]

Morning Peter & Brinzlee

I sent them an email late last night fingers crossed hope to get a reply today.

Peter, being you have a direct contact at Trig, if you are able to find out any info, that would be much appreciated as I know they can take some time in replying to emails.

Allan 

I've taken the below from the Trig Installation manual, so not sure who could be in the wrong  , although wiring diagram say something different.
________
5.6.12 Ground Returns
There are only 5 ground pins on the 25 way connector, at pins 1, 9, 10, 19 and 22. A full wiring loom with speaker, two headsets, two microphones, the TC90 connection, power and ground requires 9 ground connections. It is therefore necessary to double up connections to ground pins. This is usually achieved by bringing a short ground wire from a pin that then acts as a bus point inside the D shell.
________

[Admin]

Hi Allan,

A later version, does show this connected 

https://www.trig-avionics.com/library/SUP%20TY91%20003%20Issue%201%200.pdf