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LJD Sound Level Mismatch


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Posted

I did post this somewhere before, but it disappeared!

I've got an LJD Dedicated 4 with audio with an Aritech RD3000AGC as the mic in the room. If I connect the mic directly the TVs audio input on the scart the sound quality is perfect. If I connect it through the DVR it 'pops' or 'peaks' or something like that, (you'll get the idea in a mo).

Looking at the technical bit the DVRs audio output level is 4.7Vpp and the scart expects around 0.5Vpp. From this it appears that the Aritech is sending a low Vpp to the DVR and the DVR is amplifying it.

Has anyone experienced any similar problems or know of anything that'll fix it, I'm not adverse to building something myself if I have to but I would rather an off the shelf line level adjuster or somesuch if possible.

Many Thanks.

Posted

The only reason I was thinking the fault was with the DVR was the fact that with the mic connected directly to the monitor it's perfect. It's only when the DVR is connected in to the line the problem occurs.

Although thinking about it, it could be the MIC level is fine but the way DVR alters it causes the problem.

I'm just going to have a read through the CPC catalogue for a bit of inspiration! The customer wants more internal and external cameras, spot monitors and mics fitting but won't say yes until this is sorted. I might just order a load of different bits for audio and see if I can get any combination to work.

Guest bryan1656
Posted

I'm not familiar with the specific equipemtn that you are referring to. But out of interest, what kind of jack is on the mic?

Could it be that it is a line level (pre-amped) mic, but that the DVR is expecting a mic level and is therefore amping the already amped signal?

Either that or what are the changes in environment when you switch from the TV to the DVR? Is anything getting exposed to some other RFI or EMI when you run it to the DVR?

Posted

The mic inputs and outputs are 3.5mm jack sockets. The mic works with line level inputs on the TV so I don't think that's the problem, (although I still haven't managed to get any sense out of LJD so I'm only guessing at the moment as to what the actual audio in\out spec is meant to be).

The DVR is sat in a cupboard, on it's own, with nothing else near it other than the TV, although I did have the same problem when it was connected to another test monitor before the TV arrived on site.

I've managed to find some fixed attenuators so I'm going to try a random selection and see which works.

Guest bryan1656
Posted

Alot of speculation here, but I'm enjoying learning through the problem solving ...:D

If the mike works fine on the monitor line level, then it is likely a pre-amped line level (1V p-t-p) mic.

If the DVR is expecting a mic level (non pre-amped, <10mV) signal, then it is then amplifying it. So you could have an amped signal getting amped again.

Most of the DVRs I've seen have both MIC (level) and LINE LEVEL inputs. The tell-tale signs of a mic level is a 2.5 jack, with line level being RCA connectors. However, usual jack sizes and connectors may be a different in the U.K. <so... I dunno.>

Does the DVR have a set up wizard? Some DVRs have a set up or a configuration utility.

And the manual should specify if you'll need a mic level or a line level audio input.

Of course, the problem could also be with the DVR output. Since the mic is working on the other units, but then running it throught the DVR you get problems... the mic could still be working fine, but something is up with the output.

Do you have a known good mic that you can test with the DVR? If the mic seems to work on everything but the DVR, then it might be the DVR and not the mike.

Hmmm just ignore me if I am not helpful.... but I just LOVE troubleshooting! :)

Posted
If the mike works fine on the monitor line level, then it is likely a pre-amped line level (1V p-t-p) mic.

If the DVR is expecting a mic level (non pre-amped, <10mV) signal, then it is then amplifying it. So you could have an amped signal getting amped again.

30828[/snapback]

This bit seems to make sense, I didn't realise there were 2 variations of line level. This does sound like it could be a cause. Think I'll start with attenuating the mic line first, I'll let post back when I get a round tuit later in the week.

  • 4 weeks later...
Guest cctvman
Posted

Lurch,

Does the mic have level adjust ? i think you said it was the aritech chapie (whats it like turned down thru the dvr only ?

If the dvr has a line out is the audio ok on that

If the audio pops its the line level input is too high (signal) & can sometimes be the impedence of the mic as well !!!!

What i would do is get it set for dvr first then from there take it to the monitor (normally no audio amp in an monitor) so amp required or a tv which do have audio amps.

Get some resistors & play with that @ the dvr input side !!!!!!

You can email of board & i will pass on my mobile number handy when on site as long as it's not 3am

Regards

Cctvman

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