Noise/hum in signal chain

When playing electric guitars and basses I'm having problems with hum:
1--noise in my amps (amps are solid state)
2--with guitars or basses plugged directly into a usb interface, there is hum...more hum when the iBook is plugged in than when it is running on battery power
I've tested the guitars, pickups, and cables sufficiently to rule them out as the source. There isn't hum when recording acoustic instruments and voice with microphones.
This leads me to believe there's an issue with the electric in my room/house. I don't have experience with electrical stuff, but I've heard about special power strips that address issues with grounding. Anyone have solutions/suggestions?

I unplugged the speakers cables and the noise was still there -- so it's interference, nothing from the Mac itself. It's like crackily static, and the loudness increased when the Mac started a new download.
I think it's the Wifi!
My old MPro was hardwired to ethernet but I'm using the wireless chip on the nMP until I can run cable over to it. So that radio must be pumping out enough signal to mess with the speakers, that's possible no? I also have Bluetooth turned on for the mouse.
FYI M-Audio DX-4s.

Similar Messages

Inserts and GB1, GB2, GB3 Signal Chain???

When using a mixing desk you can pick and choose where to insert any effects in the signal chain. An effect could be pre-fader, it could be post-fader, you could have an eq before a compressor. You could have an eq after a compressor. You could do both. And you can insert an eq into the sidechain of a compressor. In other words, with a mixing desk and outboard gear you have many choices as to how to consruct your signal chain and signal flow.
Can it make a difference? Yes!
So my question is "How does GB do the signal chain?"
Are there any graphical represenations or flow charts of how GB's signal chain works?
How much control do the users have with GB plug-ins over setting up their signal chain?
Is the signal chain the same for all the GB's? GB1, GB2, and GB3? What are the differences, if any?
Any light on the subject of GB inserts, plug-ins, and signal chain would be appreciated. Thanks.
Cheers.

Hello, everybody!
This is my first post.
I was wanting to know about the signal chain too. I took HangTime's suggestion and tried it. Echo and Phaser were hard to distinguish simultaneously. So, I tried both pulldowns set to Parametric EQ and turned everything off. Turning up any Hz value played faintly and equally for each. Then, I set both to 0 dB (no change in EQ) across the board and set the track volume to just below clipping. I boosted one frequency on one of the effects until the track editor showed clipping. Then, I lowered the other effect by the same amount for that frequency and it returned to normal. I switched the order of effects and did the same thing with the same result. It appears that the two effects with the pulldown menues each effect the track equally, and they sum to zero if you boost one and cut the other the same amount. (Try the 10-band tab, it's easier.) Likewise, the standard EQ effect beneath the pulldowns worked in tandem with the pulldowns. They seem to sum.
I couldn't tell about the echoes and phase shifter. It was too hard to hear a difference. Something tells me there's a prescribed algorithm involved here, and it doesn't matter in what order you select the effects, or what order they appear. I wonder what the answer really is. My Apogee isn't supposed to dither to 16-bit more than once in a chain, for example, if compression is applied after the first dithering. So, if I want to compress twice, I have to do it once on the way in.
ManyToons . . . is......is......is ON!!!!!

How can we find the noise in the signal?

How can we find the noise in the signal, then use this inverted noise to cancel the noise in order to obtain the desired signal?

Hello astroboy,
it all depends on your signal...
Easy approach: make a low pass filter (running average or similar). This will filter out high frequency noise (in my experience the common case).
Best regards,
GerdW
Best regards,
GerdW
CLAD, using 2009SP1 + LV2011SP1 + LV2014SP1 on WinXP+Win7+cRIO
Kudos are welcome

5672 - How to add noise to QAM signal

Hi everybody,
I use the 5672 PXIe generator for creating a QAM signal with an user defined constallation set. Since I need continuous streaming I take advantage of the OSP of the 5672. I simply send the low-rate IQ - information symbols and the extensive oversampling and pulse-shaping is performed using the onboard signal processing unit. Everything works well.
Now, I want to add white gaussian noise to my signal. For my physical understanding, I would have to add the noise samples to the signal AFTER oversampling and pulse-shaping. Since this operation is done in hardware, I can not go this way. What I am doing right now is as follows: I simply add the noise samples to my low rate IQ-information symbols (BEFORE oversampling and pulse-shaping).
Has anyone an idea, how to overcome this wrongdoing I am aware of?
Thanks for all replies
Stefan

Hi Andy,
the information symbol rate (which means the IQ rate BEFORE oversampling and pulse shaping) is about 150 kSymbols / sec. As a benefit of this pretty low rate, we are able to generate information symbols continiously including all scrambling and coding operations.
Actually, your suggestion seems to be the only solution to add white noise to the signal. From my understanding, adding the noise to the information symbols results in loss of the "white" (uncorrelated) property of the noise due to the filtering operation (pulse-shaping).
Maybe for next generation of signal generator devices of NI: It would be a great feature of the OSP to add impairments like noise to the signal for purpose of testing the performance of receiver devices. Actually, this is the application we run.
Thanks for your help
Stefan

I am getting about 50 mV of noise in a signal that ranges from 0V to 5V.

I am using a BNC-2120 board with a PCI-6024E card and Labview 5.1.1. to aquire a voltage signal with a high limit of 5V and lower limit of 0V. The signal is noisy with about 50 mV of noise. Is there a way to get rid of this noise?
Thank you for you help.

George;
Noise is a difficult topic. There are some techniques that migh help you to reduce the noise level of the data acquired.
There is a good application note that you can find from at Web site which talks about that. The name of the App Note is "Field Wiring and Noise Considerations for Analog Signals". To download that one, go to www.ni.com and type in +field +wire at the search field.
Hope this helps.
Filipe

Removing Florescent Light Noise "Hum" from Audio Tracks using FCEHD

I have some clips taken under florescent lighting where the hum was discernable even during the sound check. (I was using external Electro Voice hypercardiod XLR mikes plugged into my Sony DCRVX2100, powered through a surge protector, monitoring the audio with Bose QC2 headphones). Using the same camera, cables, and mikes under incandescent lighting that day was fine - no hum.
Attempting to filter out the hum using the FCE Hum filter wasn't dramatically effective, even with repeated tests establishing that using a frequency of 60 hz, a Q of 40, a gain of -48, and the 1st and 3rd harmonics provided the most benefit.
Additionally I tried again with the FCE 31 band EQ filter, anticipating that the 50 hz and 60 hz filters would provide very specific improvements. Also tried were the LowPass Filter and the 3 band EQ.
I'd like to clean up the otherwise fine audio - any suggestions? I am considering buying a filtered power conditioner as I know that some of the problem can be "dirty" electricity resulting from the ballast of the florescent lighting.
Also, I noted that the numeric values shown for the gain using the FCE 31 band EQ filter oftentimes lagged behind the setting of the slider: returning the slider to the middle "0" position frequently didn't change the previous value of the gain shown. Is this another indication that I should just upgrade from my PowerBook G4 with 2 Gig of RAM?
Thanks!
James Mackay

Hello Jim,
And welcome to the Final Cut Express forum.
You are correct that the ballast generates the hum. Power conditioning is probably not going to reduce or eliminate it, because the old ballasts are magnetic. The only way I found to eliminate fluorescent noise at the source is to replace the ballast with an electronic one or replace the entire fixture with a T8 unit (they use electronic ballasts).
Removing that hum probably can't be done in FCE. Sound Soap can probably do it however, with it's ability to +learn noise+ and then remove that specific audio. The regular Sound Soap works as a plugin for Final Cut, which enables you to apply it within FCE.
At present there is also an 'SE' version available at 50% off however it only works in standalone mode, which means you would have to export the audio track from FCE, clean it and then re-import back into FCE.

Noise from DAQ signals sent through a 2532 switch

Hello,
I may have a hopeless case here, but it's worth a shot....
I am trying to send DAQ analog voltage time traces through a 2532b switch, and then to my DUT. When I measure the DUT without the switch, my noise level is very low. When I route signals through the switch to the DUT, the noise is increased (as expected) but to a degree that makes this system totally useless for my application. Is the 2532 not designed to route analog signals? Can I hope to send analog signals through my switch with say a doubling in noise instead of a 15x increase in noise?
I have posted a schematic of how my system is configured. Note that wherever possible, I am using BNCs. I even threaded the 2532 ribbon cables through a 1/2 in. tinned copper braid, so the system is about as well shielded as is possible with this hardware. I've also posted signal sent to the DUT (in this case a dummy 1Mohm resistor) using a 1Mhz sampling rate.
Thanks, everyone!
Attachments:
setup.png ‏23 KB
no switch.PNG ‏72 KB
with switch (2).PNG ‏75 KB

Hi Frank,
Sorry I should have included more information. The DAQ is outputting a voltage signal, for example a 1Hz 1V sin wave. This signal serves as the external voltage source for a potentiostat, such that the potentiostat sources the signal it receives from the DAQ. The potentistat has hi and low leads (working electrode and counter electrode) which are routed through the switch before going to the DUT. The potentiostat then measures the actual applied voltage and the measured current and outputs them as voltage signals which are fed directly into the DAQ.
The breakout boxes are all shielded and so are the cables. The DUT is in a faraday cage.
As far as noise sources, the building ground is not terrific but it is pretty good. 60hz noise is present, but the fft spectrum of the noisy signal also contains prominent signals at 80kHz and higher. The potentiostat is designed for high bandwidth, low current applicaitons and so has very favorable noise. The PXIe is the only computer on in the room, and all electronics are plugged into a isolated power supply (it think it is generically called a UPS). I've turned off all other equipment in the room including the lights.
Anyways, the noise only shows up when I route the signal from the potentiostat through the switch. When I send the signal from the potentiostat directly to the DUT, the noise is great (see attachments in previous posts). I would blame the extra noise on a ground loop except that as I have set it up, routing the signal through the switch does not introduce any extra paths to ground.
Thanks for taking a look at this!
-Gim

Normalize or compression

This normalizing stuff... it sounds a bit funny to me. Does it really just optimize the volume, or does it do a little compression also?
Any opinions?

{quote:title=**** wrote:}
[Normalization is] generally meant to be used on the whole project or album rather then individual tracks.{quote}
Huh... Most of my uses of normalizing are used pre-master. Often I get samples or recordings that don't have enough digital dynamic range to mix with, so I normalize them first.
IMO ears make better level decisions.
Hehe, "IMO Ears", the new Apple killer-app
Christian is an orchestral/chamber music listener. In technical terms, this sort of music features wide dynamic range, and can be prone to a lot of noise in the signal chain. Compression can indeed corrupt the nuance and subtlety of a conductor's interpretation of the music... if a ham-fisted engineer who doesn't know what they're doing records the piece, or if some amateur has a auto-levelling (a very poor cousin to compression) set on a recording device.
But compression can still be intelligently used in recording orchestras.
-Oro

Noise on my input signal at each reading half buffer

I use the PCI 6033E board.
Normaly, my signal is around 0 Volt, but at each reading half buffer, I receive a noise, and my signal come back to zero.
I find this problem on Channel 2.
Thank's in advance for your help.
Best regards

Hi,
Have you the same problem with other channel, or only with channel 2 ?
If you make a test in Measurement & automation explorer (Test panel) in continuous mode, have you the same problem ?
Perhaps channel 2 in your board is broken.
You can test your board with DAQ diagnostic utility : http://digital.ni.com/softlib.nsf/websearch/FEA4D55E1B3DA33A86257076006AA260?opendocument&node=13206...
And after, you can call National Instrument to repair this, if your board has a problem.
Regards,
Christophe S.
FSE East of France І Certified LabVIEW Associate Developer І National Instruments France

Signal-to-Noise ratio from Power Spectrum?

Hi,
I have a feeling this is a basic issue but for some reason I'm not getting it. I hope this forum can help.
I have a Power Spectrum (freq on the x-axis and power on the y-axis) and I am trying to determine the signal to noist ratio of the rf signal live.
I am using LV 8.5 and have the spectrum toolkit and am using an RFSA in a PXI chassis.
Any suggestions?
Thanks
- rf curious

Hi Rf Curious,
This questions does not have a simple
answer but let me share my thoughts and you can decide what it makes
most sense for your application. For signal to noise ratio (SNR) you
should have ideally the power of the signal and divide it by the power
of the noise. The problem here is that you are looking at both at the
same time (rf live signal). Depending of what type of signal is it, you
can recreate it and substract it from the spectrum (you will need to
recreate the phase and magnitude and delete it from the phase and
magnitude of the spectrum). This is normally done with simple signals
such as a tone.
If you don't have access to the magnitude and
phase of the data, and you only see the spectrum, then you will have to
do things different. You can probably measure the power of the signal
by measuring the power of the band where the signal is located. Then,
you can terminate your input and measure the power of the noise of the
instrument (with same attenuation and RBW settings) and have a rough
estimate. This method should have better results when S >> N. You
can also take the adjacent channel (or further) noise reference.
Finally,
if your signal has a pretty flat spectrum, then you can only take the
difference between the noise and the signal since they both have the
same RBW.
If by now, you have found other methods, feel free to post your ideas here for any other person that come across this problem.
Regards,
Gerardo O.
RF Systems Engineering
National Instruments

DAQ Card is inducing noise on an external clock signal resulting in false triggering

I am using an optical encoder as an external clock source for analog measurements with a PCI 6036 card. The optical encoder signal is "filtered" using a Schmitt Trigger circuit and proper shielding practices are used on the encoder cable. I am using a recent version of Labview.
When the TTL square wave signal from the encoder is viewed on an oscilliscope (without the DAQ attached) it is a picture perfect square wave, nothing that would cause any problems.
When I then connect the encoder output to my PFI line (with or without the oscilliscope) I get false triggering due to intermittent (seemingly random...) high frequency noise "blips". Out of 360 expected samples, I will typically get between 2 and 6 "bonus" samples... When captured on a scope, the noise looks like a decaying sine wave and lasts for only a few us. the peak magnitude is tyically around 2 V or so as shown on the scope, which is apparently just enough to make my card grab a sample.
Since the noise is only present when the encoder signal is attached to the DAQ, it seems that the DAQ is somehow inducing noise into the signal.
I have been fighting this problem for a while now and tried the following:
1) I first tried the raw encoder signal, but then added the Schmitt trigger, increased the signal strength of the encoder lines by adding resistors to ground, double checked my shielding, etc...
2) I verified that my ground potential between my card and my conditioning circuit were not causing problems. The conditioning circuit and encoder is now powered of the card itself, which should resolve any possible problem with grounds.
3) Cursed at various inanimate objects (made me feel better but didn't help the situation)
4) Checked if I could set a minimum pulse width required to trigger off of an exernal scan clock (I can't with my hardware.)
5) Swapped my card with a card of a different type (problem is still there)
If anybody out there has some recomendations, I am open to anything.

Hello OSU_Mech_Eng,
I'm not quite sure how the DAQ card could be inducing glitches into
your digital signal. Digital signals from mechanical devices like
quadrature encoders can often be glitchy or bouncy, but your schmitt
trigger should act as a debouncing filter to clean up that digital
signal. It sounds like you have thoroughly troubleshooted this
problem, and I would recommend moving on and trying to use a counter on
your DAQ board to generate the digital signal, rathar than using the
raw signal from your encoder/schmitt trigger.
You were correct when you stated that the best way to do this is by
configuring your counter to perform retriggerable pulse
generation. You can use the signal of from your encoder to gate
the internal clock on your DAQ card, creating a clean digital
signal. By setting the minimum pulse width of the signal, you
will be able to ignore the small glitches in your signal. Here is
a link to some Knowledgebases describing how to do this:
How Do I Remove Glitches or Add a Debounce Filter to My Digital Signal?
How Do I Define the Parameters for Pulse Generation in NI-DAQmx?
For further reference, on all of NI's new M-Series DAQ cards (PCI
625x), the PFI circuitry contains built in debouncing filters to
protect against small glitches in digital signals. If you have an
M-Series card lying around, it might be helpful to give that a try.
I hope this helps,
Travis Gorkin
Applications Engineering
National Instruments
www.ni.com/support

State space and noise models of a signal

Hello
I would like to apply Kalman filter to the signal in the attached file. I am asking how to generate the required matrices for the space state and noise models, which I should input to the filter.
It is my first exposure to this subject,and I much appreciate simple explanations and a practical help.
Thank you
Attachments:
Signal 2.xlsx ‏10 KB

Yeah, unfortunately I don't think I'll be able to make it down to Austin for the conference.
But more importantly, I don’t think I completely solved my curve fitting problem. The curve fitting vi that I am using isn’t generating the output that I was expecting. My goal is to simply add noise to a signal, then reconstruct the signal finding the best fit line/curve, which best represents the original signal. Here is where I currently stand:
The frequency of the new graph is too high. A sinc function is produced, but it doesn’t share the same form as the original signal.
I've tried other options, such as the Levenberg-Marquardt method, but this is proving to be a bit difficult to understand. I will attach the curve_fitting.vi and the Levenberg-Marquardt example that I was looking at. I think the LM vi is very close to what I need, but I’m having trouble integrating my own numbers into the program, to generate the results that I need. If anyone has any advice with the curve fitting, or any information that might 'dumb-down' some of the sub vi's in the Levenberg-Marquardt program model, it would help me out.
Attachments:
SimpleFit.zip ‏147 KB
curve_fitting.vi ‏163 KB

Adding white noise to signal

Hi,
I am trying to figure out how to allow a user to add white noise to a signal, the idea is that the user would enter the noise ratio in db which I would then apply to a signal measurement before displaying it. I looked at the add gaussian white noise vis in LV but I am not sure how to go from the noise ratio that the user enters to the seed and standard deviation inputs for the function.
I tried to look online but all I found was ways to add noise based on amplitude, is there a way to convert from the db ratio to amplitude given that I do not know the amplitude information of my original signal before hand since it is being sampled in real-time. Any information about this would be greatly appriciated i realize that I might be mis-understanding the way signal/noise processing really works.
Thank you,
A

dB is a dimensionless relative measure, you need a reference intensity in order to calculate it
Often times in electronics you see things referenced to 1 mW, called dBm = 10 log10(P / 1mW), so P = 10^(dBm/20)
http://en.wikipedia.org/wiki/DBm
For sound dB SPL = 20 log10(I / I0), I (intensity) is usually expressed Pascalls I0 is nearly always referencec to human hearing threshold, which is 2 * 10^-5 Pa. Multiply by your mic gain to convert to from pressure to volts.

My PH m7160n Desktop PC the power supply make high noise no signal to the monitor

my PH Media Center m7160n desktop PC the power supply make loud noise and no signal to the monitor I already replace the power supply but still the same, Thanks
Davilea

Hello @davilea,
I understand that you are getting a loud noise from your computer and a 'No Signal' message on your HP Media Center m7160n Desktop PC's monitor. As you have already replaced the power supply I will provide you with the HP Support document: Flat Panel Monitor Displays Message about No Signal, Signal out of Range, Sleep, or Power Save, which should help you resolve the 'No Signal' message.
Please re-post if you require additional support. Thank you for posting on the HP Forums. Have a great day!
Please click the "Thumbs Up" on the bottom right of this post to say thank you if you appreciate the support I provide!
Also be sure to mark my post as “Accept as Solution" if you feel my post solved your issue, it will help others who face the same challenge find the same solution.
Dunidar
I work on behalf of HP
Find out a bit more about me by checking out my profile!
"Customers don’t expect you to be perfect. They do expect you to fix things when they go wrong." ~ Donald Porter

Help diagnose this noise

So i just bought a presonus firebox earlier and hooked it up. love it already. but im still getting some of the line-noise thats been bugging me when i try to record my electric guitar directly in. I've uploaded this file, and im having a hard time diagnosing where the noise is coming from, whether its DC hum or anything else that could produce noise. ive got no CRT's in the room, or flourescant lights, or anything the room that would produce noise like this.
here's the file, and a walkthrough of what im doing throughout the test.
http://www.bedrock-studios.com/noise.mp3
:00 - :07 idling, volume knob on guitar at full (noiseless pickups), 1/4" line from guitar to presonus firebox input, presonus preamp boosted to 0 db.
:07 - :13 plucked E string
:14 - :17 cracked down preamp gain knob on firebox to -infinity (noise still present)
:23 disconnected 1/4" line from guitar (noise still present)
:30 disconnected 1/4" line from instrument input on firebox (noise still present, barely)
:37 - :39 cranking UP preamp gain knob on firebox (noise returns)
so its like the noise is inside the unit, and has nothing to do with line interference from my guitar.... is this what DC hum sounds like? could it be bad wiring in my wall outlet? or a bad presonus firebox? or is this just to be expected under these circumstances?
am i doing something wrong?
many thanks for any help
chris

I think the guitar amp simulator is the thing generating the noise. Using that kind of plug to try to demonstrate a noise problem isn't the way to go. You want to record the cleanest signal path to determine how much noise may or may not be present.
Do another test: here you're going to make 4 separate recordings.
First, take the dist. plug and any other plugs out of the signal chain (bypass or remove them). Don't plug the guitar in. Turn the firebox's gain all the way down. Record a few seconds of that sound (which is nothing. That's right, you're going to record nothing).
Next, turn the firebox's preamp up to zero dB. Record a few seconds of that.
Next, plug the guitar in, preamp = all the way down. Record a few seconds.
Then turn the preamp up to zero dB (guitar still plugged in byt don't play it). Record a few seconds of that.
Now you have four recordings. Space them apart in your arrange page by a second or so. Then use the glue tool to put it all together.
Next, go into the sample editor and use the "change gain" function to boost the level of your audio file by 12 dB and post that.

Noise/hum in signal chain

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