Anfontan
Banned by eurt
I would have to agree that its from a low frequency outside source-maybe some kind of comunications in the airwaves. The waveform sure looks low frequency-but you would need an O'scope to figure the range.
bouldersoundguy
Well-known member
It's pretty much all below 30Hz.
The part without the interference:
The part with the interference:
U
Unclejohnny
New member
I got to the bottom of it! Thank you everybody for your thoughtful help on this.
It was the shock mount! The elastic had slowly deteriorated after years of near daily use plus, the thing you twist to hold it at the angle you want had worn down.
I had compensated by adjusting the boom to a straight up and down position and it finally got to the point that the shock mount basket with no more bounce to it came into contact with the boom. I restrung it with rubber bands and reset the boom in a more typical position. Problem solved!
I'm half a block from the elevated train and sometimes I can feel it shake this hundred year or so old house so it was that and other random things causing the real low frequency vibrations that got in the mic. Bobbsy was on to something when he got a copy of the mp3 that I showed in the screen shot and said it had a lot of low frequency energy in it.(I'm editing now because it wasn't till after I posted this that I saw the further exploration of real low freq as the possible culprit by Boulder Sound Guy, Gecko, and Anfontan and I want to acknowledge you guys, too)
I came home from the music store with a new interface that has a separate power source from the USB because they thought that might be it. I hooked it up, turned it on and sat there watching it record, looking for the freaky wave and then I bumped the mic cable and noticed it made a very similar shape. Then I tapped the mic stand. Same thing! That led to taking a closer look at the shock mount. Returning the new interface tomorrow!
It was the shock mount! The elastic had slowly deteriorated after years of near daily use plus, the thing you twist to hold it at the angle you want had worn down.
I had compensated by adjusting the boom to a straight up and down position and it finally got to the point that the shock mount basket with no more bounce to it came into contact with the boom. I restrung it with rubber bands and reset the boom in a more typical position. Problem solved!
I'm half a block from the elevated train and sometimes I can feel it shake this hundred year or so old house so it was that and other random things causing the real low frequency vibrations that got in the mic. Bobbsy was on to something when he got a copy of the mp3 that I showed in the screen shot and said it had a lot of low frequency energy in it.(I'm editing now because it wasn't till after I posted this that I saw the further exploration of real low freq as the possible culprit by Boulder Sound Guy, Gecko, and Anfontan and I want to acknowledge you guys, too)
I came home from the music store with a new interface that has a separate power source from the USB because they thought that might be it. I hooked it up, turned it on and sat there watching it record, looking for the freaky wave and then I bumped the mic cable and noticed it made a very similar shape. Then I tapped the mic stand. Same thing! That led to taking a closer look at the shock mount. Returning the new interface tomorrow!
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JimmyS1969
MOODerator
Glad you figured it out! I still like the giggles. 
Bobbsy
Boring Old Git
Glad you got there!
That would have been hard to guess not knowing you lived near a train line but it's so obvious when you say it.
I should have though of that, especially as I once designed a TV studio facility in a building adjacent to the north London train line and had to spend gazillions of pounds on isolation to keep a similar vibration (the nuclear waste trains were the worst) out of the studio area.
Congratulations!
That would have been hard to guess not knowing you lived near a train line but it's so obvious when you say it.
I should have though of that, especially as I once designed a TV studio facility in a building adjacent to the north London train line and had to spend gazillions of pounds on isolation to keep a similar vibration (the nuclear waste trains were the worst) out of the studio area.
Congratulations!
Bobbsy
Boring Old Git
Just as an aside, I told the various people I asked for advice about the eventual solution and one came back with the reply:
"So, basically his mic had become a seismograph". I thought you might like that one!
"So, basically his mic had become a seismograph". I thought you might like that one!
PRHunt
I void warranties
Bobbsy
Boring Old Git
Well, the quick answer is you pay a really good acoustic consultant, in our case SANDY BROWN ASSOCIATES who I mention because they are truly excellent and pleasant to work with.
The longer answer is that it was the classic "box within a box" and "floating floor" arrangement. The whole of both studio complexes (studio, control rooms, etc) were built on a separate concrete slab which was supported on hundreds/thousands of posts with flexible rubber sections in the middle that act a bit like a shock mount on a mic. The posts were then covered with metal shuttering and several inches of concrete poured on top. Once this was all set and cured, one concrete block wall was built on the floating section and a second concrete block wall was built outside this, down the structural floor. Sandy Brown's people drove the contractors mad by ensuring that there were absolutely NO connections between the two walls. Doors and windows were all doubled (one on the inner wall, one on the outer) with the usual magnetic seals and rubber gaskets. Cable connections to the outside world were through offset flexible conduits sealed with mini sandbags when everything was run.
I can't honestly remember the isolation spec we were working to (in those days you had to pass "code of practice" testing to be allowed to feed the ITV network in the UK) but we passed with flying colours thanks to the acousticians. I do know that we had live rock bands in the bigger studio on a few occasions and, despite 100dB(A) levels in the studio, you couldn't here anything outside.
I just had a look on the Sandy Brown website and, despite the job being more than 20 years ago, we're still LISTED AS A CLIENT.
Alas, not much of this would be practical in a home studio though!
The longer answer is that it was the classic "box within a box" and "floating floor" arrangement. The whole of both studio complexes (studio, control rooms, etc) were built on a separate concrete slab which was supported on hundreds/thousands of posts with flexible rubber sections in the middle that act a bit like a shock mount on a mic. The posts were then covered with metal shuttering and several inches of concrete poured on top. Once this was all set and cured, one concrete block wall was built on the floating section and a second concrete block wall was built outside this, down the structural floor. Sandy Brown's people drove the contractors mad by ensuring that there were absolutely NO connections between the two walls. Doors and windows were all doubled (one on the inner wall, one on the outer) with the usual magnetic seals and rubber gaskets. Cable connections to the outside world were through offset flexible conduits sealed with mini sandbags when everything was run.
I can't honestly remember the isolation spec we were working to (in those days you had to pass "code of practice" testing to be allowed to feed the ITV network in the UK) but we passed with flying colours thanks to the acousticians. I do know that we had live rock bands in the bigger studio on a few occasions and, despite 100dB(A) levels in the studio, you couldn't here anything outside.
I just had a look on the Sandy Brown website and, despite the job being more than 20 years ago, we're still LISTED AS A CLIENT.
Alas, not much of this would be practical in a home studio though!
PRHunt
I void warranties
You were obviously a highly regarded client! Thanks for the interesting read!
Maybe, but it would be the the mother of all home studios...
Paul
Maybe, but it would be the the mother of all home studios...
Paul
RawDepth
New member
I disagree. Indeed it would. The study and practice of isolating structural-born vibrations would benefit thousands of home studios. I understand that many individuals can't afford high-dollar earth work and construction such as your project. But, there are dozens of little things which can contribute to sound isolation in the home...(not to be confused with room treatment for controlling reflections.)