Batboard

This is a recording my CDM1250 while responding to a dump truck fire the other day. The audio sucks and I'm not sure where to start looking for the problem.

http://www.kb1fpd.com/k-drive/matt-cdm-audio.wav

Matt,
I was able to understand you fine, although the audio was a little bit bassy. Was this the recording off the console?

Dave

rocketman wrote:Matt,
I was able to understand you fine, although the audio was a little bit bassy.

I disagree, I was able to understand, but it did sound like crap, and I had to replay it to be certain. The siren was really loud on the recording, I wonder if the loudness of the siren combined with mic agc was the problem.

The mic AGC was set for 33 or something along those lines. I backed it down to the default 28.5. Maybe that was the problem. I won't be able to check a recording of it until I get up to the firehouse again later this evening. The recording is off a tone remote base and all other radio traffic sounds perfect.

I think the siren audio is overloading the radio tx audio.

Here are a couple of sugestions.

1) Where is the siren speaker mounted. Best performance is mounted on the front bumper with nothing in front of it. Behind the grille is second best. In the lightbar is the wost.

2) Lower the tx gain in software.

The siren is in my grill pointing straight out. There is nothing in front of it but the very open grill so it might as well be outside on the front bumper. I had the windows rolled up. The siren audio in that recording is pretty quiet compared to when the window is down. I will check the audio recording tommorow to see if it made an improvement. I had some radio chatter today and the dispatcher said I sounded better. He said during that call, it sounded like I was eating the mic. We'll see what the recording tells.

I would say that your mic gain and or the TX deviation is high. Without a service monitor
to actually measure the TX, it is hard to make a solid guess.

Most radios come with way too much mic gain. You probably could hold the mic at arms
length and still be able to have heavy audio with what I hear. That is much too much.
All this does is bring out all the background noise and hence you hear the siren real loud.

Jim

Personal opinion, on Fire trucks or anything with a siren or loud airhorns, turn the audio gain down as far as possible. Humans tend to talk louder when a siren is sounding in the background. I know , I do it. Plus the urgency of the situation, and just because we want to overpower the background noise. Also it sounds like you have the mic in your throat, back off about 1-2 inches, you may also want to consider, installing headsets with mics. We have them, I don't remember the manufacturer, but it has helped a lot.

Well, this is my personal vehicle so I don't think I'll be installing a headset system

Yikes, that is terrible. It sounds to me like you're over-modulating so I'd check that. I would agree about the AGC as well. AGC sucks on analog radios I've found. Try turning AGC off and make sure Low-Level Expansion is turned off as well.

This is the one thing I hate about the Waris series. There's too many options to screw with TX and RX audio. Ever wonder why an HT600 sounds better than most radios these days?

If all the radios are warris series (HT750/1250/1550 CDM750/1250/1550) AND you are running narrowband, then low level expansion works pretty good, but as bellersley said, turn it off.

Also as a follow-up to the speaker behind the grilee (and I realise this is a personal vehicle so not much choice), you would be amazed at how much audio bounce back you have in the cab with just a speaker grille in front of it.

Any results back from your testing so far?

Turning the mic gain back down to the default 28 made it a little better but there is still obviously a tuning problem.

I understood you every time. It wasn't real clear though, and the dispatcher may not be getting the same audio as the recording source. I have heard lots of traffic on the scanner that I could understand, but the dispatcher was having trouble. Some dispatchers are better than others at "wanting" to understand a bad signal.

I like to have a radio person listen on simplex and then I blow the squelch wide open a high volume on another radio in the cab while talking, and have them report.

Just for another data point, although it maybe wasn't the best audio ever, I had no trouble understanding you either time.

Start with changing the mike gain to either 19.5 or 21. That is where we start with all WARIS radios and have never had a problem. The default mike gain is WAY TOO high.

Make sure ALL companding is turned off. That feature sucks anyway.

I'll concur with turning the default audio level WAY down....on an HT1550XLS this means 21 or so. Especially true for accessory mic gain.
The 1550's appear to mush the audio the harder you hit them.

We have 60 HT1500XLS's, all bought at once. They have all been back to M to have an audio problem fixed....that being a noisy cap somewhere in the audio section that gets noisy and creates a noise floor in the audio section. When this happens, the tx audio gets really mushy and the level drops. It is high enough that the noise floor on the transmit audio will drive voting crazy.

It's my experience that the tx audio on the 1550's is more mushy than the tx audio on a 1250, however it is crisp and good using an external audio accessory like a headset.

Greg Carttar