Problem with low signal on mic

  • Thread starter Thread starter zan1976
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The OP did mention light dimmers...

Might be interesting for OP to check noise with dimmer at minimum and at maximum, and then with all lights with dimmers turned off?
 
Starting to get confused here... This technical talk about slopes is all Greek to me, and I'm Greek, too! :D
Can we please get back to the "what I should do" topic? Do we understand what causes the noise at least? I'll try that with the dimmer in a moment. Should it be with the mic disconnected again?
 
zan1976 said:
Starting to get confused here... This technical talk about slopes is all Greek to me, and I'm Greek, too! :D
Can we please get back to the "what I should do" topic? Do we understand what causes the noise at least? I'll try that with the dimmer in a moment. Should it be with the mic disconnected again?
Click to expand...

The interface needs to have something plugged in to it to assess noise. Best is a shorting plug as described earlier, but you likely do not have that. (If you can solder or know someone who can, make up a male xlr plug connector with a 150 ohm metal film resistor soldered across pins 2 and 3. No cable on this plug)

So, yes, mic connected.

I do wonder if the usb isolator I posted earlier might help.

Anyway, get some audio with the dimmers on and off as suggested above, and see what it shows. Remember, when you record with dimmer off, make sure that every light with a dimmer at your place is switched off.
 
PRHunt said:
The interface needs to have something plugged in to it to assess noise. Best is a shorting plug as described earlier, but you likely do not have that. (If you can solder or know someone who can, make up a male xlr plug connector with a 150 ohm metal film resistor soldered across pins 2 and 3. No cable on this plug)

So, yes, mic connected.

I do wonder if the usb isolator I posted earlier might help.

Anyway, get some audio with the dimmers on and off as suggested above, and see what it shows. Remember, when you record with dimmer off, make sure that every light with a dimmer at your place is switched off.
Click to expand...

So I'm attaching three files, the one with the dimmer all the way up, the other with the dimmer all the way down and the last with the dimmer disconnected. Gain was at 50%.
 

Attachments

arcaxis said:
The levels of those mp3 files are so low I can't hear any content in them with my monitors and just barely with headphones. Did you notice any perceptible change in the noise with the different dimmer settings?

I still contend the noise appears to sound like room noise either that the mic is picking up directly or through the mic stand. The fact that the mouse clicks were picked up during the first noise sample is leading me to think the mic is quite sensitive to room noise. Even in my own room I'm surprised what a mic picks up that I can't readily hear.

zan can you unmount the mic from the stand and remove it from the shockmount and wrap it up in a pillow or similar to block it from any room noise and see if you get the noise or a change in how it sounds?
Click to expand...

Attaching file with pillow wrapped around mic, gain at 75%, dimmer disconnected
 

Attachments

Aha!
The 50Hz spike has gone. As have all the other harmonics and the "mess" around 5-10kHz. The average level is also higher, 1kH being 6dB up on the other responses. Still a LPfilter response.

But you still do not have any wanted signal to speak of?

Have you checked yet for 48volts at the mic end XLR?

Dave.
 
In the previous attachments, I definitely noticed a buzz in the "up" as opposed to "down" and "off", no discernible difference between "down" and "off" though.
 
attaching file with flute (sorry about my sound, haven't warmed up yet!)
 

Attachments

Ah, maybe that has worked?

I turned the file into a .wav and rhen ran it through a HPF set at 100Hz. It is averaging about -20dBFS which is fine (especially if the original .wav was 24bits?) and the rms noise is below -60dBFS but there is a cyclic noise bouncing around, PC fan?

Dave. Nice TOOON btw!
 

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ecc83 said:
Ah, maybe that has worked?

I turned the file into a .wav and rhen ran it through a HPF set at 100Hz. It is averaging about -20dBFS which is fine (especially if the original .wav was 24bits?) and the rms noise is below -60dBFS but there is a cyclic noise bouncing around, PC fan?

Dave. Nice TOOON btw!
Click to expand...

Damn! Forgot to turn the fan controller down! Here's the flute with the fans turned off. Would you say this qualifies as a decent recording now? Would the gizmo providing more power to the usb further enhance the quality? This was with gain at 25%. Original wav is 24 bits, 48 MHz.

Btw, TOOON was Chick Corea's "Armando's Rhumba", check it out!
 

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Last edited:
Better but you still have something blipping away there!

It is hitting a peak of -43dBish every 2 seconds or so.

If I don't fall asleep (V old y'know) after me dinner I will chop it out and try to post it.

Dave.
 
ecc83 said:
Better but you still have something blipping away there!

It is hitting a peak of -43dBish every 2 seconds or so.

If I don't fall asleep (V old y'know) after me dinner I will chop it out and try to post it.

Dave.
Click to expand...

Yeah, I think it's me knocking around. If we're talking about a "bloink" sound at around 2 sec into the track I posted, that's me hitting a key of the flute without blowing, producing a sound often used in avant-garde music (here's it's just awkward "preparing to play" on my part). As John Lennon used to say before he met Yoko: "Avant-garde is french for BS". ;)
 
zan1976 said:
Would the gizmo providing more power to the usb further enhance the quality? This was with gain at 25%. Original wav is 24 bits, 48 MHz.
Click to expand...

Having read more closely the information about the isolators, I see that they only operates at USB full speed mode (12 megabits/sec), not USB High Speed (480 megabits/second). This may or may not be a problem - I don't know. If you poke around the system information in Windows, you might be able to find out the speed mode at which the device operates.

Have a look also at this product: https://www.olimex.com/Products/Modules/Interface/USB-ISO/

You can use this in a powered hub, I think, or plug in a separate power supply. But I suspect that your powered usb port might be sufficient. At €30 (+delivery), is it too costly to experiment?
 
zan1976 said:
Starting to get confused here... This technical talk about slopes is all Greek to me, and I'm Greek, too! :D
Click to expand...
Quote of the week, that one !

Incidentally, this thread has been a masterclass in locating and solving a problem.
Been a great and informative read.
 
grimtraveller said:
Quote of the week, that one !

Incidentally, this thread has been a masterclass in locating and solving a problem.
Been a great and informative read.
Click to expand...

Yes, it has been a learning experience for me too. I think I'll try my luck with the power usb for now and if I decide to take another step, I may start another thread exclusively on usb isolators, keeping in mind PRHunt's suggestions. I'd like to thank everyone who took time to deal with my problem. This forum rocks!
:guitar:
 
Check cable first.
Check Phantom power - is it switched ON ?
Check your mic (together with cable) on another mixer, possibly mic is not working at all (membrane sticked, electronics defect, lost contact at connector, etc.), this is not hi-end brand...

USB powering problem can be a reason, but this case something would not work at all.
* Mic is additional load of power.
 
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