zeitgeist wrote:Closing_Logo wrote:zeoevil wrote:Does anybody have any idea what this is? He says it is Catalog 3 but yeah. We know how that usually goes.
The alternating current hum at the very beginning is at 60 hz. This wasn't made in the UK unless the recording is sped up.
I am eager to hear out an explanation for this post in all honesty, considering I have no idea what you mean, and you've been here far longer than myself while making less than 30 posts.
Electricity and magnetism go hand in hand: where you have one, you have the other. Electrical equipment throws out electromagnetic emissions, which float through the air, hit other electrical equipment and turn back into electrical signals. In audio equipment you've got the powerful mains power supply coming in, some kind of transformer that steps down from mains voltage to something under 12v, stuff happens to it, and it gets squirted out an audio lead to your recording equipment. If that's an analog audio chain, you're looking at about a 3V audio signal.
Now think about the mains power supply. Compared to your 3V audio signal, it's huge, in the UK 240V, in the US 110V. And the means of converting down from mains voltage to circuit voltage is with a transformer.
What's a transformer? A series of coils wrapped around a metal core. Or to put it in other terms, an electromagnet! If you created one on the bench, this thing would be kicking out electromagnetic interference like crazy when you turned on the power. Which is why they're usually so well shielded, or in power bricks away from the low voltage electronics.
Where things aren't properly shielded, the electromagnetic field can interact with another lower voltage part of the circuitry and interfere with the signal later on in the chain. You can hear this when it happens. What does it sound like? Well that depends what's making the interference. If it's your mobile phone, for example, sending out pulses of 900Mhz radio waves when it rings (radio is just another form of electromagnetic signal), it sounds like a pulsed high pitch noise. The step down transformer for a mains power supply gives out a different sound. The power coming in is alternating current, cycling smoothly around 0V - it looks exactly like a sine wave in fact. So you hear it in the audio signal as a hum.
Now, just like the mains voltage is different in different countries, the AC power supply cycles at different speeds too. In the UK, it's 50Hz, a 50 Hz sine wave. In the US, it's 60Hz. So if you hear mains hum on an audio signal, you can listen to its pitch and work out the speed of the wave, and from that you can guess where it was recorded.
You'd imagine that in scotland where the boys are, if you heard mains hum on the track it'd be 50hz. If you hear a 60Hz hum, that suggests it came from elsewhere, like for instance the USA.
*long breath out* so, that's what he meant. Here ends the lesson on electromagnetic interference and mains hum
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