Constant high-pitched humming, buzzing, whining

[kaynemcgladrey]

I'm not a genius but I can see there's sound recorded above 60Hz; heck, it's above 40Hz (your church organ example).

My impression is that the Apple tech did NOT even reproduce my line-in test, and that the attached analysis of the 5 seconds of 'silence' via the USB mic shows the problem. Do you agree, or is it the background noise?

When you did the iPod - Cable - Mac test, was that cable common to any of the other activities? Like if you thought about it, any time you had the noise, you were using that cable? A broken cable could cause problems like this.

No, that was a cable that I use to connect my iPod to a car. Used for nothing else.

The pictures were produced in Audacity 1.3.7. Open the sample under test. Select it. Analyze > Plot Spectrum. Reset the dials on the bottom of the window to the numbers in the pictures.

Here's the result on the five seconds of sound using the USB microphone at the Apple store.

We do differ in that I'm using the Television sound standard 48000, 16-bit, Stereo. I'm using Audacity 1.3.8 on one machine and 1.3.7 on the other. If you have an advanced enough Mac, there is no Audacity 1.2 any more. Intel/Leopard will not reliably run Audacity 1.2.

Using 1.3.8 here.

-- You do empty the trash, right? I occasionally dig somebody out of trouble by doing that. The Trash Can is a real location on your desktop and it takes drive space.

Yes.

-- Do you run Mac Janitor? Mac OS-X eventually gets clogged with its own logging files and they need to be cleaned up.
http://personalpages.tds.net/~brian_hill/downloads.html

No. Machine runs maintenance scripts itself. 10.5.8.

-- Are you using iTunes to create Music CDs? Left to its own devices, iTunes will compress your work to an internal format and then uncompress it back out to the CD. You can change iTunes import preferences to change that. Later on, you can change iTunes preferences back (I use iTunes Plus 256-Stereo AAC) and tell iTunes to convert your work to that -- after you make the CD. That will give you a perfect Music CD and a compressed iPod version of the work.

[/quote]
I don't use CDs at all.

[kozikowski]

<<<My impression is that the Apple tech did NOT even reproduce my line-in test, and that the attached analysis of the 5 seconds of 'silence' via the USB mic shows the problem. Do you agree, or is it the background noise?>>>

Analog testing is very difficult to do. The analog amplifier part of a USB microphone is inside the USB microphone case and once the microphone makes the digital bitstream, generally, no more noise increase is possible (I know you can get clocking errors, but that's usually in really big installations).

Also, not all USB microphones can be turned off. So that's the noise profile of the store and the USB microphone. It has nothing to do with your problem, but both events have the word "Sound" in them, so that will have to do.

The built-in microphone has a microphone amplifier and other processing and is also, in general, completely separate from the Line-In electronics.

You do have to be careful with the analysis tool because the numbers on the edges are fluid. Note that big hump is at 10 Hz (bottom edge). 10 Hz isn't sound. Nobody can hear that, so that doesn't contribute to the show at all. Energy has to appear between 20 Hz and 20,000 Hz to count. To hear the 20 Hz number you have to be a dog, and the 20,000 Hz number you have to be a very young woman from Nebraska.

The next biggest hump is around 130 Hz and it's level is -63dB. 60dB is roughly the limit of human hearing and all the rest of the humps are way below that. So whatever they used for a microphone isn't half bad. But the test has nothing to do with you.

You have to extract the numbers from the graph to compare the performances. Alternately, you can redraw the graph (on paper) with the real numbers on the left and bottom, and then transfer all the blue waves over to it. Audacity keeps magnifying the graph to fit the work. That's not what you want when you're trying to compare two performances. That might be a feature request.....

I'd be curious the iPod test on the loaner machine. I've been able to do this test successfully on an iBook, and PowerBook and now on the MacBookPro, so it's not a fluke.

Koz

[kozikowski]

<<<No. Machine runs maintenance scripts itself. 10.5.8.>>>

You leave your machine on and lit up 24/7? I know Systems Operators at work that actually do that. I don't believe "periodic" runs on a sleeping machine. Most people let their machines fall asleep.

Koz

[steve]

To hear the 20 Hz number you have to be a dog, and the 20,000 Hz number you have to be a very young woman from Nebraska.

I don't think dogs can hear 20Hz, though Wales and Elephants can. Dogs, human children and bats can hear 20kHz.

Other than that - as Koz says.

Personally I think that it is pretty rubbish that you reported a fault with the "Line In" and they did not test the "Line In".

Can you guys compare recording on similar machines from the Line-In input with NOTHING plugged in? (and the record levels set to sensible levels). You should both get very low level noise. Most audio inputs (assuming they are not gated) will have their maximum noise level with nothing connected, and their lowest noise floor when short circuit.

It is safe to short circuit a line level input (but for any Windows users, do NOT short your microphone input - it has voltage on it! )

[kozikowski]

<<<you reported a fault with the "Line In" and they did not test the "Line In".>>>

Which is why I asked in an earlier post exactly what you said when you walked into the Apple Store. Your goal is to fix your production and their goal is to prove there's nothing wrong with the Mac, so choice of words is paramount.

<<<20Hz, though Wales and Elephants can.>>>

Whales can hear it, too. Dogs respond to the long alpha waves ahead of an earthquake long before anybody else can "hear" them.

<<<Can you guys compare recording on similar machines from the Line-In input with NOTHING plugged in?>>>

The Line-In on a modern Mac is both Analog and Optical Digital. The plug tells the machine which to use. You can hear it switching if you pay attention.

--------------------thp-- "esting One Two Three Testing.."

<<<their lowest noise floor when short circuit.>>>

Most people don't have a short circuit laying around, but everybody has an iPod, so plugging in an iPod turned off with a short, known, good cable is the easiest way to produce a stable condition for testing.

Throwing the colume control all the way up is also a known stable reference point. I don't think the Mac actually has gain -- most computers don't. That merely conditions the input for unity gain -- but I haven't actually checked that yet.

Koz

[steve]

Dogs respond to the long alpha waves ahead of an earthquake long before anybody else can "hear" them.

I'm not a dog owner and 'quakes are rare here so I'll take your word for it

Most people don't have a short circuit laying around, but everybody has an iPod

I guess I'm not "most people"

The Line-In on a modern Mac is both Analog and Optical Digital. The plug tells the machine which to use.

Neat - SPDIF I presume?

[kozikowski]

<<<I'm not a dog owner and 'quakes are rare here so I'll take your word for it >>>

Dogs are pretty instant about it. You suddenly realize that the dog is not holding a dialog with you any more. The tail is wrong, the ears are wrong, the motion is wrong. If you do manage to catch their eyes, there is no doubt Something Very Serious Is Up.

Asking about quakes is a lot like asking "How's your boat?" Grab a nice cuppa and settle down.

I have a little angle bracket and about a foot long, tiny metal ball, key chain hanging somewhere in each room. They (and everything else not nailed down) will start to sway.

I went through a moderate quake once in a room that had no motion reference at all. Zero. It was a very mild quake but I nearly revisited lunch because where I saw the walls and floor and where they actually were in physical space was different.

<<<I guess I'm not "most people">>>

You are allowed to plug in your Consumer Electronic Product with a 3.5mm headphone socket. Hopefully, battery operated. You don't want the mains in the measurement.

<<<Neat - SPDIF I presume?>>>

Yes. There's no shortage of people trying to figure out how to interface that with their actual SPDIF equipment. I think the low record is three adapters.

Koz

[kaynemcgladrey]

I was in a conversation recently where I made the comment, "and I hate how when they've fixed it, they never post the solution".

Realized that I'd done that. This post is an attempt to fix that. If your MacBook Pro seems to produce rubbish sound, you're in the right place.

Tried recording on a 17" MacBook Pro, an iMac G5, a loaner MacBook Pro (15"), and a Sony MP3 IC Recorder ICD-UX70.

On all Macintosh equipment the line-in port was unsuitably quiet using a variety of powered and non-powered microphones. The 17" MacBook Pro also produced a variety of electrical interference that was not seen in the other units.

On all Macintosh equipment the USB port was unsuitably quiet using a variety of microphones.

In all tests the system preferences for input devices was cranked up, moved down, and otherwise jiggled.

The Sony MP3 IC Recorder ICD-UX70, on the other hand, produces minimally noisy sound using a variety of microphones. This noise is easily and readily removed using Audacity on OS X 10.5. Produced stellar sound by comparison, and in a peer review of samples from all units under identical conditions using identical microphones and ONLY varying the recording device, the Sony won by a landslide.

Based on this I can't help but wonder what the rest of the internet is doing for their screencasting, because I couldn't recommend using a Mac for recording audio based on these tests.

[steve]

That's interesting kaynemcgladrey, and contrary to the views usually expressed by Mac owners.
Could you upload some samples somewhere on the internet and post links? Having no direct experience of audio on Macs I'd be interested in hearing the test results.

[kaynemcgladrey]

There are many samples linked throughout the prior forum posts on this subject. Just scroll up - maybe page 1 or page 2.

The Apple Store claimed that the audio was of acceptable quality. I have a large number of customers (for online training) who have said the audio is of unacceptable quality. I'm going with the paying customers on this one.