[Jerry, W5BFF]

My repeater configuration:
TX Radio: Motorola Radius M120
RX Radio: Motorola Radius M10
CPU: Raspberry Pi 2
Generic USB Soundcard (5.1)
Easy Digi Interface as described on the “Getting Started – Hardware” page

I had the repeater up and operational using a HamGadgets ID-O-Matic IV as the controller, but I replaced it last week after I built up this interface.

The audio coming in through Echolink sounds GREAT! The audio coming in via RF sounds not so great. I recorded new .wav files for the repeater ID, and although I ran them through Adobe Audition and matched volume, sample rate, size, etc of the samples provided, it doesn’t sound stellar.

My biggest issue is the latency during full-duplex audio. The lag is so bad that when I ID, I’ll hear most of my call sign coming through after I let up from the PTT on my microphone. I’ve tried using the asla configuration utility to adjust volume and tone… which improved the volume in the output, but did nothing for the audio quality or latency.

I’ve tried googling fixes, but the best I could come up with was it’s a RPi hardware issue. Is anybody else having the same experience? Is there something I can do to fix it?

Thanks!

-=Jerry A. Goodson=- W5BFF
http://www.ka5ahs.org

[Aaron, N3MBH]

Some audio latency is to be expected as it is doing a A/D conversion, processing the audio, then doing D/A conversion. I don’t think I’ve heard of it being that slow.

As for the audio distortion, that sounds like it could be overdriven audio on either the receive or transmit side. You might be able to determine that by other audio. You said the EchoLink audio sounds fine, so that would lead me to believe it’s on the RX side. If you have a speak level output going into a mic level input on your sound card (even with the isolation transformers) you can easily clip the audio or possibly damage the sound card.

If that is the case you would probably need an inline attenuator circuit. I believe the typical difference between line level signals and mic level signals is about 1000:1. A speaker output into a mic input could be even greater.

I’d try taking your USB sound card and plugging it straight into your PC. Use your audio recording software to test the recorded audio from your RX. Then while you are at it you can play back a know good file to your TX side and check that independently. That might help you narrow down you circuitry and if you have any hardware issues with you sound card.

73,
Aaron – N3MBH / WRFV871

OpenRepeater is offered free of charge. Find out how you can support us.

[Mauro, IW3ROW]

For distortion, also be sure to remove the MIC Boost/AGC option in alsamixer (sudo alsamixer->F5->select the mic boost option->press m->ESC).

My USB dongle MIC input is driven by the radio line output and the MIC input level is set to about 1-3%.

Regarding the in/out audio delay, in my case with Rpi3 is around 800ms/1s maximum. It’s acceptable, but sometimes can be annoying, I’m wondering if there is any setting or workaround to decrease that delay as much as possible.

Mauro IW3ROW

[Jerry, W5BFF]

Audio quality (not distortion just tone balance) is something I can tweak… my main concern was the audio delay.

With my CPU running at 900MHz, I’m hearing my whole call sign echoed back to me this morning.

I was wondering if there was a way to split of the A/D <-> D/A processing onto a soundcard processor so that it wasn’t so resource-intensive on the Pi itself?

…and I wonder if the BBB does any better?

[Jerry, W5BFF]

UPDATE: Regarding audio quality, I followed the advice in this thread >> https://openrepeater.com/forums/topic/new-parameters-for-general-repeater-settings-concerning-ctcss-and-dtmf-decode << and it INSTANTLY cured that problem.

Now I can focus on full duplex audio latency. So far, I’ve tried to hard code my CPU frequency to 900MHz, but I’m still showing it to drop to 600MHz at times.

While my audio quality is superb, I’m still having quite a delay in repeater operations…

[Mauro, IW3ROW]

About the delay, I guess also the usb audio card affects the result. Now I’m using a cheap generic usb audio dongle with C-MEDIA chipset. In the coming days I’ll experiemnt with different audio cards like the BEHRINGER UCA202 that I already used on rpi for projects related to audio streaming: http://www.music-group.com/Categories/Behringer/Computer-Audio/Audio-Interfaces/UCA202/p/P0484

I’m also thinking to use the usb card as input and rpi integrated audio as output and see what happens in terms of audio delay, just an idea involving two separate devices for in/out.

Mauro IW3ROW

[Jerry, W5BFF]

Doing some googling, I found a NO_REPEAT switch that will allow bypassing the audio to be regurgitated from the CPU.

I’m still mulling over the COR/COS and PTT functions of an ID-O-Matic IV, and controlling them with SVXLink while letting the audio to pass through the ID-O-Matic. I’d still want audio to go in/out through the soundcard for Echolink, and I’d want to use ORP for the courtesy tone, ID/announcement, and DTMF macros.

If I can marry the two together, I may just figure out how to get the best of both worlds.

[Jerry, W5BFF]

IT WORKED! Well…. sorta….

I had to do a lot of experimenting and swapping, but where I’m at right now is this:

COR/COS is routed to the RPi 2 and the ID-O-Matic (The I-O-M just so the controller knows to pass audio. I don’t know if it’s necessary, but I have an LED that indicates carrier present by turning red. All other controller functions in the I-O-M have been disabled)

I bypassed the Easy Digi for the audio I/O. The audio is parallel coming in and going out from the radios with the soundcard audio. The audio is routed through an ID-O-Matic, thus eliminating the audio delay I was experiencing by routing the full duplex audio through the RPi 2.

Before bypassing the Easy Digi for audio isolation, I was having a real hard time balancing the RF vs Net audio. When I bypassed the Easy Digi and just ran the audio parallel, I brought the RPi audio level up to the same as the audio from the RX radio. There just seemed to be too much loss sending the audio through the isolation transformers.

Between the RPi, the I-O-M, and the Easy Digi, I have a pile of wiry mess. I want to redraw a single PCB that has the components the Easy Digi and I-O-M that I need from each with a 40-pin GPIO header that will make a nice tidy single RPi hat.

Before sinking that much effort into the project, I may check out the existing SVXLink Card kit and see if the proverbial wheel has already been invented… but that’s what I’ve figured out to this point.

[Aaron, N3MBH]

Sounds good, and glad you made some progress. You can check out the availability of the SVXLink Card here: https://shop.f5uii.net/en/ They tend to do group orders and are working on their second order now.

A full schematic of the SVXLink card can be found here: https://openrepeater.com/wp-content/uploads/2016/04/schema_svxlink-rasp2015.pdf

If you want to build it yourself. It is done in a block format so you can tweak the design to your liking.

Right now ORP is still in development and is experimental so it still requires some knowhow and a willingness to tinker to get things to each persons own likings.

73,
Aaron – N3MBH / WRFV871

OpenRepeater is offered free of charge. Find out how you can support us.

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