24" iMac 3,o6 has a low frequency undulating hum/drone

I can only rid myself of this very annoying drone or hum if I place the imac in sleep mode or shut down. It is not a fan noise and ofter reading the forums I turned off the build in mike all to no avail. Any suggestions would be appreciated
iKarl

Hi iKarl
Welcome to Apple Discussions
Run the display brightness up and down, if the humming stops at the maximum setting then we have nailed it down to the display inverter (dimmer rheostat) control. If in indeed the inverter is the culprit then you'll really need and should take your iMac in for service.
As a work around set the iMac's brightness to max. and use the third party utility Shades for dimming the display!
http://www.versiontracker.com/dyn/moreinfo/macosx/31515
Dennis

Similar Messages

27" iMac screen low frequency humming + moving too freely on the base

Got a new 27 incher on tuesday after fedex lost the first one That's a different story.
The problems
1. The huge iMac moves a tad bit too freely on its base and when i try to tilt it to an angle, it doesn't stay at that angle it trys to go tilt back down ... maybe its gravity.. i don't know...
2. Very very low frequency humming noise from the iMac top left corner... its out when it goes to sleep. not the normal HDD/fan noise. I have a fan app, its not the fan... but its really annoying when working on it ...
i've seen a couple of posts about this. i'm taking this 27 incher to the store tomorrow... lets see how the geniuses deal with it. i hope they acknowledge this problem. does anyone else with the 27" have this problem?

Took it to the apple store, some genuises looked at it, confirmed it and sent me another one

My headphone audio output on imac makes a very loud low freg buzzing sound.

I have my Imac hooked up to my home studio for recording music. It is currently hooked up to my high quality rane mixer, which has superior sound quality. But for some reason every time I plug a cord into the headphone jack to my mixer, TV or anything else from the Imac headphone jack, it comes out with a very loud low frequency humming/buzzing noise even on very low volume settings, even with the bass turned all the way down. It is extremely annoying. Does anyone else have this problem? I would expect a little more from apple products. Especially with something simple like this, since these machines are mostly designed for video/audio production. . I have tried switching my cords around and changing my setup for months now. No luck. And, no, my imac does not have an optical out and I think that would probably solve the whole problem. Any ideas would be greatly appreciated. Thank you for reading.

Welcome to the Apple Discussions!
Do you have your recording equipment isolated from the computer equipment? These buzzes and rumbles are usually easily solved by making sure that your audio equipment is plugged into a different electrical circuit than the iMac.
However, yes your iMac does indeed have digital audio. I do not know of an Intel model that does not have digital audio. The audio ports do both analog and digital audio. To use digital audio you need a Toslink cable with a miniplug adapter on the iMac end of the cable.
Such as this;
http://www.amazon.com/gp/product/B00016W6Y6/pfrd_s=lpo-top-stripe-1&pf_rd_t=201&pf_rd_i=B00016W67I&pf_rd_m=ATVPDKIKX0DER&pf_rdr=063C32X7YE311VH2T7WY
Dah•veed

Intel 20" iMac hard drive has failed, what can I do?

Hello everyone,
My white 20" iMac (late 2006) has just died and I think the hard drive might be irreparable.
Yesterday it wouldn't boot up and froze on the grey screen, however it worked fine from a safe boot. But today it would not boot at all, not even in safe mode. So I booted from the original OSX Tiger discs and ran Disk Utility. I tried to repair the disc permissions but this failed and told me the disc needed repairing so I hit Repair Disk. This also failed, saying the disk could not be repaired and must be erased and to reinstall the OS.
Is there anything I can do to rescue my hard drive? (I backed up about a week ago so I'm ok... ish)
Or will I have to visit an Apple store for a genius to have a go?
Does anyone know what might cause this sort of failure? Is it just substandard parts reaching their retirement age?
Also, does anyone know how much a replacement HD is likely to cost me?
Thanks for any help and suggestions.

simon.goodwin wrote:
I'm afraid that in the end the hard drive was 'too old' as the genius put it.
Is it really too much to ask for a hard drive to last more than four years?
That's on the low end, but not entirely unusual. "Normal" lives seem to vary fairly widely.
Also, I was not at all impressed by the competence of the genius I dealt with. He didn't even know how to boot in safe mode or from an external drive.
Yeah, in my limited experience, they vary, too, but that's rather basic. Must be a newbie.
I am now up and running with two backups in place.
Yay!
Also, I have given the failed hard drive to a friend who will try and recover the last weeks data for me as the Apple genius said he didn't know how to do that either.
That's a specialty Apple doesn't do, at least not in most stores. See [Data Recovery|http://web.me.com/pondini/AppleTips/Recover.html]. The services that do it have (expensive) specialized hardware and software.
Needless to say I am not happy with Apple's hardware or customer care.
I'd agree about the "Genius," but not necessarily the life of the drive.

How do I get the line-in to record low frequencies?

The iPhone with GarageBand is potentially one of the most powerful tools for mobile recording ever. Unfortunately there are several tragic yet avoidable drawbacks that reduce it to nothing more than a mere toy. 1. You can't use the camera usb adapter to bring in loss-less digital stereo input. 2. Even if you could, you can't split the stereo into 2 seperate mono tracks. And to take the cake... 3. You can't do much recording with the 3.5 jack's line-in because you get ABSOLUTELY NO LOWS! This is due to the iPhones roll-off low frequency limiter filter, which i'm told since ios6 can possibly be disabled, though it's not in the Settings and i have yet to find an app that will do it in the background while running Garageband. Sure, the Garageband app could do that, but then it would be a powerful incalculably valuable tool in the hands of everyone. No lows means no drums, no bass, and vocals that sound like...well...like they were recorded via telephone. Yes, it's painfully clear you recorded that demo on a phone, because when you play it back in your home or car it sounds like your listening to someone play it for you on the other end of a phone call. There is no adjustment to compensate for the absence of low frequencies. SOMEONE PLEASE TELL ME I AM WRONG and that you have a work-around or know of something I've missed. How do you get lows into Garageband???

Thanks for the info. I am not wanting flat stereo nor digital input from the 3.5. Only wanting flat mono. But before I go the apogee route (which is a $150-200 solution, not to mention a solution that will add more devices to the connection and thus more opportunities for noise), I will probably just resort to purchasing an ipad (can get a mini for $299) . My mixer has usb out, and I can go straight into the ipad digitally with the usb camera kit, albeit I still can't split 1 stereo channel into 2 mono channels. But I digress: my entire purpose for this post is that i would like to stay as mobile as possible by using the iphone, but with all the darn limitations imposed by no one other than Apple, what could be an easy way to record has been nullified. What's frustrating is that all the components are there and I have them, all the hardware is more than capable; but in both cases (the 3.5 mono or the usb stereo) there is a software feature (or lack thereof) blocking me.
Again if anyone knows of an app that will disable the software low-cut, please respond...

Low frequency measurement (1 to 5 Hz) issues - Reg

Hello All,
i am facing a problem in measuring Low-Frequencies in the range of 1-5 Hz. I am using VIs used for pulse-width measurement and the card is PCI-6031E. i am generating frequency using PCI-6013 card.
Actually i am trying to develop an application for measuring the speed (RPM) of the motor which runs very slowly. so if i miss one pulse per second also, when i multiply that with 60 it will be big error.
So if any can give me a solution that will be big help to my issues.
Thanks.

Hello sathiskumar,
I'm not sure what you mean by missing a pulse but I think what is
happening is that your counter is rolling over and starting to count
from zero again. Every time the counter rolls over, it will
output a pulse. You can connect this signal to another counter
and count how many times your first counter has rolled over. That
way, if you don't receive a pulse on your first counter before your
counter rolls over, the second counter will have a record of how many
times this has happened.
I hope this helps!
Eric
DE For Life!

Why am I getting very high values for the very low frequency region of a random signal?

I am tyring to produce a power spectrum graph for a Tachogram data, related to Heart Rate Variability Analysis. This data can be thought to be as a random signal, but has a frequency spectrum range of 0 - 1HZ.
The problem that I am facing is, I am getting very high values for very low frequency region, closer to DC value. Even the DC value is really high, in the range 10^8. It is suppose to be a low number. Any suggestions would be appreciated.
Thanks.

Here is what my work is all about. I am trying to develop a software for Heart Rate Variability analysis. I am not sure if you are aware of heart beat waveforms, they are bunch spikes, occuring at irregular intervals. We have to do analysis on this waveform. How ? First we have to create a plot called Tachogram. This is done by, for example, let's name the first spike R1, the second one R2, and the third one R3, and so on. This is how the co-ordinate points are created. (R1, R2-R1), (R2, R3-R2), and so on...
Here R1 is the time instant at which the spike R1 occurs, and R2-R1 is the time difference between these peak occurences. So, if we plot these values, then it gives us one like what you saw on your time domain plot. What we have to do with this signal is, we have to apply FFT technique to produce its power spectrum for analysis. Generally the frequency range of the spectrum goes from 0 - 0.5 Hz. They part this range into VLF, LF, and HF, and analyze how much power is distributed in these regions. The distribution would tell you if you were stressed out,or have worked out, things like that. Normally, you can view spikes around LF, HF region. If you had viewed the power spectrum for the data that I sent, then that's what it pretty much looks like. I think I have said a lot about it now. Hope you get it.
We were talking about the "other component", I can't really see where it lies, must be in the 60-80 sec. range in the graph. If you look at the spectrum, I am getting a huge value around 0.0033 Hz, how do I minimize or remove this ?
Also, I am using Unevenly Spaced Signal Spectrum.vi, I am not sure what excactly is the unit for the Power Spectrum output. Technical Papers denote, Periodogram algorithm used by this VI, gives Power Spectral Density ? If that's right, then the unit is V^2/HZ.
Please advise.
Again, I should thank you for your time and effort.
I have to meet a deadline this week in finishing this project, and your help is immense to me at this point.
Thanks & Best Regards,

Logic cuts low frequencies when recording audio?

I am using a Lexicon Lambda interface and a iMac running Logic Pro 9, when i try to rip vinyl from a single turntable or record a mix from my mixer logic cuts most of the low frequencies leaving a tinny sounding recording, i have tried recording using the same interface with a Acer laptop running both Cubase and Soundforge and all is fine, so it must be something in Logic's settings, probably something simple that i have missed most likely, anyone know what to do to stop this?

Sounds as though you are hearing the effect of the RIAA EQ curve (bass cut and treble boost) applied at the cutting stage to keep the cutter head excursion within manageable bounds. If you connect a deck directly to your computer, this is to be expected. However, a DJ mixture should correct for the EQ. Does it have more than one output? If so, see if changing output affects the sound. If not, does your interface have a 'phono' input? If so, this should provide the required compensation. Failing that, does anyone have a Linear Phase EQ preset to deal with the RIAA curve?

A slice of low frequencies and A strangled sound

Good afternoon!
My Envy dv6-7377er has a problem with the quality of the sound.
When I connect the laptop to the amp, I notice a slice of low frequencies and A strangled sound.
When I connect my old computer or CD is no such problem.
No "Beats" equalizers do not eliminate the problem.
What should I do to get good sound?
Sorry for modest vocabulary and bad grammatik, I'm from Russia, and can not clearly explain the problem.
But I beleve, you uderstand me.

Hello Oleg_P.
You should try removing the driver and allowing the operating system to reinstall it. Try the following.
Navigate to your Device Manager.
Expand the "Sound, video, and game controllers" section.
Right click on your sound card and select "Uninstall."
Reboot the computer and allow Windows to complete the reinstallation.
Post the result.
Have a great day!
Please click the white star under my name to give me Kudos as a way to say "Thanks!"
Click the "Accept as Solution" button if I resolve your issue.

Distortion with low frequency sounds

I'm using a X-Fi XtremeGamer soundcard in a Gigabyte GA-P35-DS3L MOBO running windows vista 32bit,? and Logitech X-540 speakers with monster cable RCA cables.
About a month ago I started noticing that low frequencies (Bass drum, explosions, bass guitar) in songs, video games, etc. were being distorted and muffled. It sounds like the sounds are coming out of a massi've amp in another room behind 3ft. of concrete.
At first I thought it was my speakers, so I replaced my old set with the brand new logitech speakers and brand new cables. No help
Then I uninstalled all my creative software and drivers, and took the card out. Switched on the integrated audio chipset on my MOBO from BIOS and downloaded the latest drivers for that. The sound quality improved slightly.
Next I uninstalled the drivers for the integrated chipset, turned off, popped the sound card back in, turned off the integrated chip,? installed the drivers from the CD, then updated with the latest? SBXF_PCDRV_LB_2_5_0006 driver. Back to the original problem.
Next I checked to make sure the sound files themselves weren't corrupted, I put the same files on another computer with the same MOBO, and they sounded fine through the integrated chipset.
So I'm out of ideas... has anyone heard of a problem like this before? It seems to me I hae a defecti've sound card, but the fact I have similar problems with the integrated chipset worries me...

I have exactly the same problem - especially with the sound track in games like Far Cry2, Fear2 etc - low frequecy sound heavily distorted, just as you describe. Same result with all settings tried. Low frequecy sound in movies is fine.
I have? a 2. speaker setup, and am wondering if something is simply not seperating frequecies correctly - trying to make the subwoofer handle? frequecies that should go to the normal speakers?
Message Edited by ArchPrime on 03-29-2009 08:3 [email protected]

One-Third Octave Filtering of Low Frequency Data

I would like to analyze steady state, low frequency (0.1Hz to 80Hz) data that has been aquire over several minutes of acquisition at a rate not exceeding 1000Hz. I am using the Third Octave Filtering Tools in the Signal Processing Toolkit, but it is unclear to me that if I just change the sample rate input into the Third Octave Filtering.vi if that will give me the octave bands that correspond to the ranges that I am interested in. Is the any other way to calculate this? For example, if I wanted to find the band power of an individual octave band, say band 0, which has a center frequency of 1Hz, how would I do that?

There is a thorough explanation of the algorithms and details of the ANSI S1.11-1986 specification to which the toolkit is built around in the reference manual for the Signal Processing Toolkit. Here is a link to it:
http://www.ni.com/pdf/manuals/322142a.pdf
On page 24-4, it explains how to calculate the center frequencies of your 1/3 Octave filter bands.
Jack Arnold
Application Engineer
National Instruments

Is it possible to detect low frequency signals with a high sampling rate?

Hello everyone,
I'm having an issue detecting low frequency signals with a high sampling rate. Shouldn't I be able to detect the frequencies as long as the sampling rate is at least 2 times the highest frequency I will measure? The frequency range I am measuring is 5-25 Hz, and I use Extract Single Tone.vi to measure the frequency. The sampling setting I am using is 2 samples at 10 kHz. Is there a method I can use to make this work?
Attached is the vi.
Attachments:
frequencytest.vi ‏21 KB

You are sampling at 10Ks/S, but only taking two samples. What do you expect to see? If your signals are binary (On or Off) you would only see either an on or an off, or if the rise/fall time was fast and you were Extremely lucky, one of each. If you want to see a waveform you have to sample for at least the period of a waveform. So you should take samples for at least 0.2 seconds to capture an entire waveform at 5Hz, ideally longer. Think of looking at a tide change at a dock. If you want to see the entire tide change you will probably have to measure repeatedly over 24 hours, not just run out on the dock, measure the height twice and leave. That wouldn't tell you anything other than at that precise moment the tide height was X, but not that it was at high tide, low tide, in between, etc.
I type too slowly, I see that a more technical answer has been given, so mine will be the philosophical one!
Putnam
Certified LabVIEW Developer
Senior Test Engineer
Currently using LV 6.1-LabVIEW 2012, RT8.5
LabVIEW Champion

Low Frequency Measurements using counter timers

I am trying to measure multiple speeds using FP-CTR-502 modules. I am having a resolution problem. Looking at the post at the following URL (http://forums.ni.com/ni/board/message?board.id=110&message.id=3601&query.id=42252#M3601) looks like exactly what I need to do, but I'm not sure how to program this. Does anyone have any example code to get me headed in the right direction?

Hi Tcrower,
Here is the example that Carl L. was describing in his forum post along with his instructions. Also, there are thorough instructions for using the program in the front panel as well as in File >> VI Properties >> Documentation.
You can measure frequency in two ways using a counter.
1) Measure the time it takes for a set number of pulses to pass or,
2) Count the number of pulses that pass in a set amount of time.
For low-frequency signals it is best to measure the time duration of a set number of pulses. If we tried to calculate the number of pulses that passed in a set amount of time, we would need a long gate period to get accurate results.
The drawback of measuring the amount of time it takes for a set number of pulses to pass is that the sample period varies with the frequency of the signal.
To accurately measure low frequencies with a CTR module, select two counter channels, one output channel, and one gate input channel. Count Input 0 counts the pulses of the signal that we are measuring. The output of the counter is set to high for x pulses and low for x pulses, which is used as the gate of Count Input 1. The source of Count Input 1 is the internal clock reference (the example can be modified to use an external clock reference). During the high phase of Count Input 0, Count Input 1 counts the pulses of the clock reference.
During the low phase, we read channel 1 and reset the counter.
For example, if the output of Count Input 0 is set to high for 4 pulses and the signal has a frequency of 20 Hz, the output of Count Input 0 is high for 200 ms. During the high phase, we will count 200 counts if we are using the 1 kHz internal clock reference. So to calculate the frequency, we have F = #pulses/duration = timebase * terminal count/counts = 1000 Hz * 4 terminal counts/200 counts = 20 Hz.
Regards,
Hal L.
Attachments:
Low_Frequency_Measurement_(CTR).zip ‏77 KB

How to connect my new MacBook Air to a LaCie hard disk with TIme Capsule backup from my old Imac? LaCie has USB 2.0, FireWire and eSata ports.

How can I connect my new MacBook Air to a LaCie hard disk with TIme Capsule backup from my old Imac? LaCie has USB 2.0, FireWire and eSata ports.

You can direct connect your MBA to the LaCie via USB 2 cable. If you have an Apple Airport Router you can USB connect the LaCie drive to the router and then use Airport Utility to configure it. Time Machine can access it either way.

Low frequency Voltage measurement

Hi,
I am using PCI 6025E to control load bank and to measure voltage, current and frequency of a generator.
While current and frequency measurement is not a problem, voltage measurement is toublesome.
Since on test bench already there are few PCI boards and huge number of sensors, I do not want to add NI 9205 or any other additional boards and clutter the area (other people are also working there).
The problem with voltage measurement is that out of three generators two run from 400 RPM to 1600 RPM i.e.. somewhat 15-55 Hz.
I had two solutions for this:
1, Putting a step down transformer (230 Vac / 5 Vac) and then measure the voltage. But when testing at somthing like 15 Hz I have to deal with magnetic saturation with commercially available transformer. I do not want to take pain to go on built my own transformer.
2, Using high precision voltage Divider. The problem is that what should be the galvanic isolation? Isolation transformer, but then again low frequency problem.
Hence could someone suggest me since there is a bit confusion in my head.
Thanks.
Solved!
Go to Solution.

If you have a sine generator (15Hz migth be hard for the soundcard ) you can do a calibration of your transformer.
(If only the voltage amplitude is of interest , use a isolated DMM as reference and run your generators)
Or you buy a isolation voltage sense amplifier. (weidmueller, phoenix, wago, ...)
Greetings from Germany
Henrik
LV since v3.1
“ground” is a convenient fantasy
'˙˙˙˙uıɐƃɐ lɐıp puɐ °06 ǝuoɥd ɹnoʎ uɹnʇ ǝsɐǝld 'ʎɹɐuıƃɐɯı sı pǝlɐıp ǝʌɐɥ noʎ ɹǝqɯnu ǝɥʇ'

24" iMac 3,o6 has a low frequency undulating hum/drone

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