Quad switch with all channel audio passthrough

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mccla5214
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Joined: Sun Sep 05, 2021 1:45 am

Quad switch with all channel audio passthrough

Post by mccla5214 » Mon Sep 20, 2021 3:00 am

Looking for a quad switch that will pass the audio from any active display on the screen. All of the units I have looked at so far only pass one channel of audio through to the output. I would like one that if I have 4 channels displayed, that all 4 channels of audio were passed through to the output.

Thanks
Mike/KA5TDA

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gm1mfn
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Re: Quad switch with all channel audio passthrough

Post by gm1mfn » Mon Sep 20, 2021 7:16 am

It sounds like you are looking for a sound mixer rather than a switch.
Doppler effect: The tendency of stupid ideas to seem smarter when they come at you rapidly.

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PA3CRX
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Re: Quad switch with all channel audio passthrough

Post by PA3CRX » Mon Sep 20, 2021 7:39 am

Would an easy audio mixer circuit not do the job for you? Like https://www.eleccircuit.com/simple-audi ... et-2n3819/

In ATV repeater PI6ATS we ran to the same issue. With analogue signals that are not always present every individual receiver will deliver audio noise. So the result after mixing is a lot of noise. We added a simple squelch circuit for each audio channel and then mixed the signals.

Hopefully this brings you on some idea’s.

Best regards,
Chris PA3CRX

mccla5214
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Re: Quad switch with all channel audio passthrough

Post by mccla5214 » Mon Sep 20, 2021 3:27 pm

Hi Chris,

That would require me to break out the HDMI audio from each source and then find a way to put it back into the HDMI stream again. Been working on that exact same issue for tying in the voice audio from a 73cm repeater to the system so people who don't have ATV systems can still participate via the standard voice repeater. It's surprisingly difficult to separate out the video and audio then put them back together again. Right now I'm looking at having to use a HDMI to RCA converter to get them split and a RCA to HDMI converter to put them back together again without losing either voice or visual quality. If I could find a quad switch that passed on the audio from any on screen image to the common output, it would be so much cleaner.

DId you actually find a way to make a squelch circuit that ran on the audio side of the world? How did you do it, with a high pass filter to separate out the high frequency audio that's present? I'd be curious to know.

Mike

g8lce
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Re: Quad switch with all channel audio passthrough

Post by g8lce » Mon Sep 20, 2021 10:15 pm

GB3NQ uses several rydes and a quad display when more than one frequency has DATV. So far we have 146.5, 437 and 1249MHz receivers. The switching of the rydes and power to the RPis is done with an Arduino. The composite video is used and the video is switched by relays. The audio goes through a 4 channel stereo mixer so a zoom type QSO can be had over the repeater as long as all parties are on different frequencies. I looked at using a HDMI quad split with a pulse to the selector buttons but that would have caused the problem with the audio that you have as the quad split only selects one audio.
Output of audio on HDMI and composite would be useful if possible.
The use of composite from the rydes seems to work well apart from the 1247MHz ryde seeming to overheat on hot days and not RX.
The steaming output of GB3NQ will be going off for a while as I am moving house on 23rd September 2021 and therefore I have to derig the aerials and the Internet will take a couple of weeks to come up again. (assuming I can get a signal at the new location - the line of site calcs say it should work!!! )

Martin G8LCE

mccla5214
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Re: Quad switch with all channel audio passthrough

Post by mccla5214 » Mon Sep 20, 2021 10:28 pm

Thanks for the information and have fun moving, did it so much in the army I got good at it, I feel your pain

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g7kpm
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Re: Quad switch with all channel audio passthrough

Post by g7kpm » Mon Sep 20, 2021 11:18 pm

Hi,

I am not aware of any HDMI quad processor that will mix audio to a common output.

We have been considering a potential HDMI future upgrade for GB3CT (as we still use analogue video) so that digital inputs remain digital and converting the analogue receivers to HDMI video, keeping the audio analogue. Do do this I was looking at extracting the audio from the digital receivers HDMI into analogue using an audio extractor box: eBay item number: 384262468112

This would then use the repeaters existing audio switching/mixing circuit within the logic unit to mix the audio from all active inputs to a common output before reinserting the analogue audio back onto the HDMI with a combiner box: eBay item number: 223780536334

CTs audio switcher/mixer is basically a simple 8 channel relay switch from Ebay which closes a relay controlled by the RX active logic line (1 per RX). I cant find the exact ones we have but this looks almost identical. 2 of 4 channel units are used for 8 channels.
eBay item number: 142651201066

The control switch was replaced with a TTL level voltage from the logic to activate any combination of relays 1 - 8 which switches inputs to a common output. If the input is inactive, then the relay for that channel is open circuit, so effectively mutes the unused channel. It's crude and simple, but works.

73s, Jason G7KPM

mccla5214
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Re: Quad switch with all channel audio passthrough

Post by mccla5214 » Mon Sep 20, 2021 11:41 pm

Thanks for the info. Looks interesting on the web site.

We were thinking the HDMI A/V converter but I like this idea better, keeps all the video in HDMI. Run the audio to a mixer (HDMI audio should be silent with no input signal). Then process the audio and put it back in with an audio inserter. This allows you to separate the L/R audio so you can feed in a separate audio stream (like the receive audio from a voice repeater) and send the audio stream to a voice repeater transmit side.

The more I mull this over in my head the better I like it.

Thanks again for a great suggestion Jason,

73,
Mike/KA5TDA

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PA3CRX
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Re: Quad switch with all channel audio passthrough

Post by PA3CRX » Tue Sep 21, 2021 9:12 am

Mike,
I wasn’t aware you had a HDMI signal present, I am living in the past century with analogue signals like composite video that I understand :lol:
You have several solutions handed over now but to come back on your question how the squelch circuit was made; it is based on an old (1975) schematic of a home made 2 mtr FM transceiver. In accordance with what you assumed indeed a simple high pass filter is used.
In our circuit we used CD4066 instead of the fet (multi channel). Simple but effective!
squelch circuit 1975.JPG
squelch circuit 1975.JPG (186.14 KiB) Viewed 3666 times
squelch circuit made by PE1RQM.JPG
squelch circuit made by PE1RQM.JPG (338.33 KiB) Viewed 3666 times
In case you want to build it: no PCB layout present :lol:

Best regards,
Chris PA3CRX

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g7kpm
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Re: Quad switch with all channel audio passthrough

Post by g7kpm » Tue Sep 21, 2021 6:21 pm

You are welcome Mike, but please keep in mind that none of the suggested equipment has been tested in practice!
I take it that this is to build a repeater?
If so, it might be worth contacting Rob M0DTS at the GB3KM group. He has been doing a lot of R&D with resect to making GB3KM fully digital, so might be better placed to offer some tied & tested ideas and equipment advice.

73s,

Jason G7KPM

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