Audacity Forum

That's fascinating. There's just a festival of things wrong with that last sample. The audible hum is only the most obvious symptom -- and even that's not "normal."

I need to beat it up a little more. Don't take anything back or buy anything else for a while.

Koz

kozikowski wrote: Don't take anything back or buy anything else for a while.

The Plantronics went back. A colleague of mine listened to the sample and said it was awful.

I am looking into an Apple Genius Bar appointment for tomorrow; the only thing consistent thus far has been the computer. And me. Happen to have a Geiger counter I could borrow to rule myself out?

Do you have an iPod? A real one? Any vintage?

How about a stereo jumper cable like this...

http://www.radioshack.com/product/index ... Id=2102949

...or this. Even better...

http://www.radioshack.com/product/index ... Id=2102970

Connect the iPod to the MBP via the short jumper cable and don't turn it on.

Close Audacity. Go into the System Preferences and make sure the Line-In Volume Control is all the way up. Do you see any of the little blue lights?

Launch Audacity and clilck once inside the red record meters. You may see bouncing. Where is it? -50, -48?
You can separate the meters from Audacity and make them very much larger.

http://kozco.com/tech/audacity/Audacity1_full.jpg

Koz

<<<I am looking into an Apple Genius Bar appointment for tomorrow>>>

They're really good, but I'd be surprised if they can figure this one out. Apple Service works by naturally assuming everything you're doing is screwed up. They divorce/disconnect the computer from the whole world and test it in a vacuum. Not a real vacuum, you know...

Then they assure you absolutely that the Mac is working perfectly.

"But what about my contract, clients, bad transfers, and destroyed video/audio/show?"

That's nice. Come back when you have a Mac problem.

So it would be nice if we could get there first. Unplug the MBP from the little wall power supply, plug in the iPod and do a noise test. This is a cousin of what they're going to do at the bar anyway.

Oh, there is one other thing they can do. "Leave it here for three or four days..."

If we can get the problem down far enough, you can start making arrangements for a replacement computer now....

Koz

Used cable; length is approx 6'.

iPod Touch 2nd gen.

No blue lines moving in Input.

No red lines moving in Audacity. Made the meters full-screen. Nada.

Pressed record in Audacity.

Recorded what *SHOULD HAVE BEEN* absolute silence, if I understand it right. iPod Touch wasn't playing music and screen was off.

Resulting tape hiss attached.

http://audacity-noise.s3.amazonaws.com/ ... nedoff.zip

Your test is significantly noisier than mine (I'm on top).





Have a good time at the genius bar.

A quick look at the numbers. 40 Hz is the frequency of one of the pedals of a church organ. You don't so much hear it as feel it. Most modern speakers won't present it.

60 Hz is the tone of the power coming out of the wall in the US.

-60 dB is reeeely, reeely quiet. It's considered the lower limit of human hearing.
-96 dB is the lower limit of any sound at all in 16-bit Stereo.

Sound doubles and halves in loudness to your ear about every 18dB.

So. On my MBP, there's no acoustical energy at all from about 40 Hz and up, and what there is of it, is at the limit of the computer to deal with it. You, on the other hand have lots going on up there. Also look at the 60Hz point. That's the power hum. It's only present at all on your picture and it's really high.


Has any of this actually worked? Do you live in a part of the country with very dry air? You may have fried the sound services with a static discharge or, goodness knows what.

You didn't tell us the bit depth. That's in the Audacity Preferences. Audacity wakes up at 32-bit Floating. I reset mine to 16-bit. Even with that error, this is way too much noise.

Koz

It's set to the default of 32 bit.

So the net net is this: my MacBook Pro is different than yours. Vastly. And no amount of noise-canceling microphones nor noise reducing software features will fix that difference sufficiently. Off to the genius bar.

I travel now and then. 26 different trips this year, and this is a slower than average year. Will find absurdly dry air in Arizona in two weeks time.

I'm curious what you're going to tell them at the GB.

Koz

I'm hoping you can run another one of those frequency spectrum analysis' or provide instructions on how to do that. There's 5 seconds of silence at the beginning of the recording, though the silence is quite relative.

http://audacity-noise.s3.amazonaws.com/applestore.zip

The technician agreed that there was tape hiss or buzzing (the sound of the electrical interference) present in the recordings I'd made. He claimed, however, to not be able to reproduce the sound, and he would not show me his test setup and would not allow me to demonstrate the issue.

Testing was conducted without me being present. The technician did his recordings using an unknown "USB mic" as well as the built-in mic. There's a lot of background noise present in their recordings but I can't determine if the 60hz electrical buzz is there. Test conditions were also unknown, though it sounds like they had it in a busy Apple store.

His final recommendation was the McBook Pro was working as designed and he recommended I use professional recording equipment.

I'm having my company's helpdesk send me a loaner computer for next Friday when I can try recording again.

<<<He claimed, however, to not be able to reproduce the sound, and he would not show me his test setup and would not allow me to demonstrate the issue.>>>

Right. That's the step where they cut the Mac off from the possibly damaged outside world and perform isolated tests.

<<<The technician did his recordings using an unknown "USB mic" as well as the built-in mic.>>>

Neither of which goes through the Line-In electronics which is what I think is broken.

<<<His final recommendation was the McBook Pro was working as designed and he recommended I use professional recording equipment.>>>

That's the kiss-off. The Mac is fine. Have a happy day.

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.


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.

I turned the input control all the way up in the Apple Preferences which turned the "microphone" control all the way up in the Audacity window. Press record.

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.


Items:

-- 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.

-- 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

-- 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.

Koz