Christian Spaeth Posted June 15, 2012 Report Share Posted June 15, 2012 I realized that on one of my SRas (block 21) that gets audio from two LMas, there is, in the distant background a strange sound periodically repeating itself, sounds like an echoy cough. In normal cirumstances it's too quiet too be audible, but if the scene is quiet I can hear it. I am wondering what it might be, I changed frequencies and put the LMa close to the receiver, still there. My other SRa (block 24) that I use with two SM Txs doesn't produce this sound. I tried both LMas, and I hear it on both. Does anybody know what this might be and how to get rid of it? Any help strongly appreciated. Here's the recording of the LMa: test.mp3 Quote Link to comment Share on other sites More sharing options...
Eric Toline Posted June 15, 2012 Report Share Posted June 15, 2012 I had to crank up my amp to hear it. It appears to be so far down in the mud as to be totally inaudible under normal circumstances. That's not to say there isn't an issue with the gear but it's not a show stopper at this point IMO. Eric Quote Link to comment Share on other sites More sharing options...
Sean McCormick Posted June 15, 2012 Report Share Posted June 15, 2012 I call that the 'ricochet' sound. Usually when I get it, it's loud and it's seems to be a quick intermod issue when a couple of transmitters cross each other a certain way. I'm curious about the repetitive pattern your sample has. Quote Link to comment Share on other sites More sharing options...
Jeff Babb Posted June 15, 2012 Report Share Posted June 15, 2012 The consistency of the pattern makes it seem that it's not crosstalk but maybe a nearby radar tower. Quote Link to comment Share on other sites More sharing options...
Christian Spaeth Posted June 17, 2012 Author Report Share Posted June 17, 2012 The consistency of the pattern makes it seem that it's not crosstalk but maybe a nearby radar tower. Interesting. I will test it in another location to see if it's the same. As I wrote before, it's not there in block 24. Quote Link to comment Share on other sites More sharing options...
LarryF Posted June 17, 2012 Report Share Posted June 17, 2012 The consistency of the pattern makes it seem that it's not crosstalk but maybe a nearby radar tower. The precise repetition has me puzzled also. It may not be happening in block 24 because it isn't an interference in block 24. It does seem like some outside interference scanning up and down in frequency and occasionally crossing the set frequency. The fact that transmitter position doesn't change it, however, makes interference seem less likely. I don't know of any process in the SR that is that slow. After you've changed locations, if it still happens, you might try a power source that feeds the SR only and no other gear. Strange one. Best, Larry F Lectro Quote Link to comment Share on other sites More sharing options...
LarryF Posted June 17, 2012 Report Share Posted June 17, 2012 You might also turn the gain all the way down on the LMa's and remove any signal source. Clutching at straws here. Larry F Quote Link to comment Share on other sites More sharing options...
LarryF Posted June 18, 2012 Report Share Posted June 18, 2012 You might also turn the gain all the way down on the LMa's and remove any signal source. Clutching at straws here. Larry F Found a big straw. The battery telemetry cycles the LMa carrier at 0.3 Hz rate or 3.3 secs per cycle. It is possible the LMa needs a fix. What are the serial numbers of your LMa's and your matching SR? Best, Larry F Lectro Quote Link to comment Share on other sites More sharing options...
Christian Spaeth Posted June 19, 2012 Author Report Share Posted June 19, 2012 I did some testing, no signal source attached to the transmitters. These are my observations: the 3.3 second cycle seems to be it. The coughing is there as soon as I turn on the LMa(s). The same sound but louder is audible once as I actually turn the LMa on or if I change a frequency. I now noticed it on one(!) of my SMas in block 24 too. Strangely enough, on the other one it's almost not audible, only if I turn it up way to max, so there it's never a problem. I also hear this sound when I touch the SMa's antenna (on both SMas). The actual signal however is never interrupted by the cough, it just overlays it. I took off the power cable from my Nomad so it only fed the SRas, but nothing changed. My LMas are US, the SRas and SMas are EU versions. I know they're not supposed to work together (US and EU) but as the same sound is audible on the SMas don't think this is the reason for it. Serials: SRa block 21: 759 SRa block 24: 827 LMas: 9141, 6146 SMas: 285 (low cough), 286 (normal cough) So I am wondering: Is this a sound that is always there, only buried so deeply that it's usually not audible? Now that I know how it sounds, of course I am more prone to noticing it than before, though I never noticed it on my last production, which also had quiet moments. And one more thing: If I change gain on the Tx, the cough doesn't seem to get louder or softer. Quote Link to comment Share on other sites More sharing options...
VASI Posted June 19, 2012 Report Share Posted June 19, 2012 Christian is not the same. Because the US version is 60Hz and EU is 50Hz. The US version is 4dB or 6dB better noise than EU. Or vice versa? I don't remember. Quote Link to comment Share on other sites More sharing options...
Christian Spaeth Posted June 20, 2012 Author Report Share Posted June 20, 2012 any news on the subject, Larry? Still hearing the sound, it's almost haunting me... Quote Link to comment Share on other sites More sharing options...
LarryF Posted June 21, 2012 Report Share Posted June 21, 2012 Christian is not the same. Because the US version is 60Hz and EU is 50Hz. The US version is 4dB or 6dB better noise than EU. Or vice versa? I don't remember. US is 75kHz and Euro is 50kHz. The US improvement is about 6 dB in most cases. It is just that much more critical that the gain be set properly (by the manual) on Euro units. Best Regards, Larry Fisher Lectrosonics Quote Link to comment Share on other sites More sharing options...
LarryF Posted June 21, 2012 Report Share Posted June 21, 2012 any news on the subject, Larry? Still hearing the sound, it's almost haunting me... The LMa's, being US spec deviation, are probably generating more of this low level noise due to different battery voltage carrier swings. US specs have a 5 kHz swing; Euros have 3 kHz swing. So your receivers are set for a 3 kHz swing while the LMa is doing 5 kHz. We will look at a filter change in the DSP of the transmitters and receivers, to see if we can reduce this some more. Best, Larry F Lectro Quote Link to comment Share on other sites More sharing options...
Christian Spaeth Posted June 21, 2012 Author Report Share Posted June 21, 2012 Thanks Larry. I hope this can be eliminated in the future. Quote Link to comment Share on other sites More sharing options...
LarryF Posted June 25, 2012 Report Share Posted June 25, 2012 Thanks Larry. I hope this can be eliminated in the future. Hi Christian, This has been done and the faint recurring swish is eliminated. Instead of using a 0.3Hz square wave for the battery telemetry and then filtering it to knock off the rough edges, the new firmware steps the leading and falling edge in 6 small steps making it a much gentler transition. This firmware can be loaded into your transmitters but I'm not sure about how to handle the US spec LMa's. You really ought to get them matched to your receivers (50 kHz deviation) so you can run the transmitter gain at an optimum level. Best, Larry F Lectro Quote Link to comment Share on other sites More sharing options...
VASI Posted June 25, 2012 Report Share Posted June 25, 2012 US is 75kHz and Euro is 50kHz. The US improvement is about 6 dB in most cases. It is just that much more critical that the gain be set properly (by the manual) on Euro units. Best Regards, Larry Fisher Lectrosonics Thank you Larry! Quote Link to comment Share on other sites More sharing options...
Christian Spaeth Posted June 26, 2012 Author Report Share Posted June 26, 2012 Thanks Larry! Awesome support and indeed great news. I couldn't find the firmware on the Lectro site - is it possible to update it myself or should I contact my dealer? Quote Link to comment Share on other sites More sharing options...
LarryF Posted June 26, 2012 Report Share Posted June 26, 2012 Thanks Larry! Awesome support and indeed great news. I couldn't find the firmware on the Lectro site - is it possible to update it myself or should I contact my dealer? Hi Christian, Probably best to use a servicing dealer since you would need a programming box. I'd also like to get your LMa deviation set properly for your Euro SRa's which will take some measurement equipment. This is the reason you noticed it on your LMa's. Anyway, email me at larryf@lectrosonics.com so we can work out the details and who to go to. We will roll this stepwise modification out as we update the various production transmitters. Best, Larry F Lectro Quote Link to comment Share on other sites More sharing options...
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