What's this - look at the waveform

hrn · 8th November 2004

A sample from a wave file I've recorded. Is it just harmonic distortion....?

Hans

JonCraig · 8th November 2004

it'd have to be something really low. is there some big 30Hz "hit" happening in the song at that point? was the bass player plugging in in the next room?

SpaceChild · 8th November 2004

Tjäna Hans,

That looks like a vocal track and a blow of air into LD condenser. I get a lot of that with one specific male vocalist. Just hipass the track.

Spacey

hrn · 9th November 2004

I had a deeper look at it. I gained the last part 20 db up and got this on a spectrum meter:

Spectrum

This is the last part of the file for listening:

Wave

I think it could be the singer stepping his foot on the floor or as SpaceChild says, some blow of air.

By the way, it's recorded with an Audix CX 101 and a Spectra Sonics pre from the sixties.

Hans

hrn · 9th November 2004

Of course....just wondered

But I'll keep it in honour for Rock and Roll

Hans

faeflora · 11th November 2004

I've also seen wierd ultra low waves like that with some digital distortion.

**Tim Farrant** · 15th November 2004

It could be that the preamp has a DC stability problem and the prescence of audio is causing DC shifts to occur which show up low frequency signals. Looking at other parts for the waveform, I think you can see the same thing happening, somewhat obscured by the higher frequency signals. If you filtered out everything above 100Hz I think you would reveal more of the same. Definitely looks electronically generated to me.

Tim

hrn · 16th November 2004

I'll have some closer looks and come back to you.

Thanks,

Hans

hrn · 16th November 2004

Tim,
When you say "the preamp has a DC stability problem ". Do you mean the power supply or is it in the preamp itself do you think?

Thanks,
Hans

**Tim Farrant** · 17th November 2004

Well I am guessing here, but what could be happening is the DC conditions of the preamp circuitry could be being "modulated" by the audio envelope, and then ringing on after the audio is gone and finally settling, hence the the little low frequency wiggle at the end of the signal clip you posted. You can see the same sort of wiggle mid way thru the waveform where the audio is at a low level.

Being a preamp from the 60's, it's possible the design is either flawed or there is something wrong with the unit - electro capacitors dried out perhaps? Is it tube or transistor this Spectra Sonics preamp?

Tim.

hrn · 18th November 2004

Tim,
It's transistor. See some pictures at the link:

Pix

Thanks,
Hans

**Tim Farrant** · 30th November 2004

Hans,

Those photos do not help me too much, do you have the circuit diagram of this mixer?

Tim.

hrn · 2nd December 2004

Thanks Tim,
I don't have the diagrams of the mixer and I have not found anything on the net either.

I called the original designer of the console Ingemar Ohlsson of Audio Data Lab http://www.audiolab.se/ (do you believe me if I say he was surprised...the thing was built at the end of the sixties) and described the problem to him.

He told me that the mixer is DC-coupled (with/using??) transformers and has a frequency response going Very high and that the problem probably is......(..try to find an English word...) a swaying...self-swaying (instability?) caused by a grounding/earthing matter.

He will send me some diagrams of it...Still had them!! Very nice guy

Hans

8th November 2004	#1
hrn Lives for gear Joined: Apr 2003 Location: Gävle, Sweden Posts: 586 Thread Starter	What's this - look at the waveform A sample from a wave file I've recorded. Is it just harmonic distortion....? Hans __________________ R1b M343 Cro-Magnon U5a Sami

8th November 2004	#2
JonCraig Lives for gear Joined: Apr 2004 Location: Nashville, TN Posts: 1,800	it'd have to be something really low. is there some big 30Hz "hit" happening in the song at that point? was the bass player plugging in in the next room? __________________ "My job is to make music sound great and to not whine too much." --George Massenburg Learn PT Techniques from Multi-Platinum Engineers. Click Here.

15th November 2004	#7
Tim Farrant Moderator Joined: Jun 2002 Location: New Zealand Posts: 2,410	It could be that the preamp has a DC stability problem and the prescence of audio is causing DC shifts to occur which show up low frequency signals. Looking at other parts for the waveform, I think you can see the same thing happening, somewhat obscured by the higher frequency signals. If you filtered out everything above 100Hz I think you would reveal more of the same. Definitely looks electronically generated to me. Tim __________________ "Come on, make my day" Dirty Harry (Clint Eastwood) Visit Buzz Audio

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8th November 2004	#3
SpaceChild Gear maniac Joined: Oct 2004 Location: UK/FI Posts: 194	Tjäna Hans, That looks like a vocal track and a blow of air into LD condenser. I get a lot of that with one specific male vocalist. Just hipass the track. Spacey

9th November 2004	#4
hrn Lives for gear Joined: Apr 2003 Location: Gävle, Sweden Posts: 586 Thread Starter	I had a deeper look at it. I gained the last part 20 db up and got this on a spectrum meter: Spectrum This is the last part of the file for listening: Wave I think it could be the singer stepping his foot on the floor or as SpaceChild says, some blow of air. By the way, it's recorded with an Audix CX 101 and a Spectra Sonics pre from the sixties. Hans

11th November 2004	#6
faeflora Lives for gear Joined: Oct 2002 Location: washington dc Posts: 2,022	I've also seen wierd ultra low waves like that with some digital distortion.

16th November 2004	#8
hrn Lives for gear Joined: Apr 2003 Location: Gävle, Sweden Posts: 586 Thread Starter	I'll have some closer looks and come back to you. Thanks, Hans

17th November 2004	#10
Tim Farrant Moderator Joined: Jun 2002 Location: New Zealand Posts: 2,410	Well I am guessing here, but what could be happening is the DC conditions of the preamp circuitry could be being "modulated" by the audio envelope, and then ringing on after the audio is gone and finally settling, hence the the little low frequency wiggle at the end of the signal clip you posted. You can see the same sort of wiggle mid way thru the waveform where the audio is at a low level. Being a preamp from the 60's, it's possible the design is either flawed or there is something wrong with the unit - electro capacitors dried out perhaps? Is it tube or transistor this Spectra Sonics preamp? Tim.

18th November 2004	#11
hrn Lives for gear Joined: Apr 2003 Location: Gävle, Sweden Posts: 586 Thread Starter	Tim, It's transistor. See some pictures at the link: Pix Thanks, Hans

30th November 2004	#12
Tim Farrant Moderator Joined: Jun 2002 Location: New Zealand Posts: 2,410	Hans, Those photos do not help me too much, do you have the circuit diagram of this mixer? Tim.

2nd December 2004	#13
hrn Lives for gear Joined: Apr 2003 Location: Gävle, Sweden Posts: 586 Thread Starter	Thanks Tim, I don't have the diagrams of the mixer and I have not found anything on the net either. I called the original designer of the console Ingemar Ohlsson of Audio Data Lab http://www.audiolab.se/ (do you believe me if I say he was surprised...the thing was built at the end of the sixties) and described the problem to him. He told me that the mixer is DC-coupled (with/using??) transformers and has a frequency response going Very high and that the problem probably is......(..try to find an English word...) a swaying...self-swaying (instability?) caused by a grounding/earthing matter. He will send me some diagrams of it...Still had them!! Very nice guy Hans