iPod -> audio recorder
For several weeks, I have been pondering the following: speakers and microphones are pretty much the same, in that they’re both bits of piezoelectric material held next to magnets with wires coming out of both sides. The only difference is that current is imposed on one and the other imposes itself on the current instead. Consequently, it seems like you could take your headphones and use them as really crappy microphones to record sound wherever you go with an MP3 player, assuming you made the correct changes to the firmware. Well, it turns out that not only is this possible, but people have already done it. In true hacker form, the first step is to install Linux on your iPod. I don’t think I’m actually going to do this in the foreseeable future, but it’s nice to know that someone else has tried it and it works.
That’s pretty cool. I knew you could use speakers as mics, but I didn’t even imagine you could use an iPod to record. That’s kind of cool. And a little creepy too. What if the people walking around on the streets, in schools, on the subway are recording my conversations? Of course, they could probably do it a lot easier with a little tape recorder.
and while you’re at it, you can use the LED’s as solar cells and (incredibly slowly) charge the battery
Wow! I didn’t know that worked!
While the physics and hacker geek in me appreciates the fact that you can record using speakers/headphones, the musician and gadget geek in me has to point out that for a long time there’s been an Apple-authorized third-party add-on that lets you record to your iPod, the original iTalk. The very latest iPod supports the new stereo iTalk that has a jack for an external microphone. They also sell iKaraoke – pretty cool!
However, the quality of the stereo iTalk is still limited by the A-D converter, which is not nearly good enough for recording live music. What I really drool over is this device: M-Audio Microtrack 24/96.
I’m intrigued by the iKaraoke. Any idea how it isolates and fades the lead vocal track? That’s a pretty neat trick.
Well, based on online review the answer is that it doesn’t do it very well at all.
There’s one really clever trick to remove lead vocals that works on maybe about 25% of pop music: just subtract the right channel from the left. The reason is that most digitally-mixed albums put the lead vocals in dead center, but pan every other channel to the left or right. So subtracting the channels completely eliminates the vocal track but leaves the rest.
For the remaining 75% of pop music and 99% of all other music, there’s no magic solution. If you can analyze the entire song you can possibly identify the parts containing the vocals and get frequency characteristics that you can filter out. But for a real-time filter you have to use some sort of crude approximation that ends up distorting everything in the process.
BTW, I still think the iKaraoke is a neat idea, but for karaoke mp3 files, not for vocal removal.