Unusual sound effect with a loop.

[longedge]

I've been listening to some Australian Aboriginal music. The subtlety and intricacy of the nuances that an expert can produce with a didgeridoo is amazing.

Just playing around, I grabbed a 15 second loop. Created a test project and put it in the global audio settings but got a very noticeable break in the loop. So next I tried it in the pre-load and the loop was unbroken.

I then tried out putting it in both the global settings and in the pre-load. I found that instead of having a 15 second loop, I've got a constantly changing and seemingly endless background sound. Because the two are out of sync, they 'beat' against each other sometimes cancelling part of the sound out and sometimes re-inforcing different parts so that as it plays it sounds totally different.

I don't imagine you could do it with many sounds, but in this case it works. Hours of sound just from a couple of hundred K - doesn't seem bad :lol

What I don't understand is why the same loop is handled differently depending on where it's placed?

[rhosk]

longedge, what is the format of the loop (wav, mp3...)? This is why Flash is powerful - takes a wav file and loops seamlessly converted to mp3. I don't know of any other program that will accomplish this. ie, MP3's are famous for adding a split second of silence at the end of the file...why? I don't know. Curious as to what you're getting at

[longedge]

Hi Ron,

Suppose really I'm just remarking on a new (to me at least) discovery. It may not be of any use to anybody else but if it is...

I saved the sound out as an ogg from CoolEdit.

It was just by chance that I tried it in the Global Setting and found that it didn't loop in there whereas it does in the page and it seems to be a constant 'slippage' between the two sounds. The rhythms and beat in the sound are complex so the 15 seconds of sound changes all the time.

The real (and completely insignificant ) point is that it acts differently in the two places in AMS.

[Protocol]

fgdfgdfg

Here's just a simple and 101 version of audio physics, but if you take a sound file and call it soundfileA then copy that sound file and call it soundfileB, then phase invert either one so that one is normal and the other is inverted, then place soundfileA on top of soundfileB...it completely disapears.

No Bermuda Triangle mystery here (although that's been explained recently as Methane deposits on the ocean floor), but it's a very useful tool. Play around with old Beatles records using this method and you can in some cases completely isolate the vocal track from the rest of the music. Being a Nine Inch Nails fan, I haven't tried this, but it's cool none-the-less.

In fact high end cables use this technique to cancel out noise in the signal as well.

Additionally, if you take one audio file and layer it on top of itself EXACTLY (sample for sample), you will roughly get a 6dB increase in overall level. This prinicple works exponentially, so you have to double it each time (i.e. not just layer one track on top of it...more in the format of 1:2:4:8:16). The cool thing is that it's an accoustic property as well. This is why a crowd is louder than a single voice. But because each voice is not exactly like the other's, you get an unpredictable, but reletively expected output level.

So...phase invert (which you can find in Cool Edit) and you will make the sound disapear...double the file and you will increase the overall level by about 6dB. In your case, since the sound is fluctuating, but has the same tonal quality it seems to get thinner and thinner until it disapears, then it comes back as a thin sound, then apears again. This is called phasing and is the behind-the-scene mechanics of that cool "flanging" sound in Lenny Kravitz's "Fly Away". The term "Flanging" comes from the technique of adding two sounds together (in most cases as an effect) by older studios who used audio tape Flanges (metal or plastic tape reels). BTW...although I'm a digital cat allll the way...nothing sounds as sweet as an analog flange. You still reading this?!

And nice catch! That knowledge of the different locations of sound placement within AMS will, indeed come in handy some day.

[longedge]

Is this a symptom of the expanding universe - a time shift :lol

[Corey]

This is called phasing and is the behind-the-scene mechanics of that cool "flanging" sound in Lenny Kravitz's "Fly Away". The term "Flanging" comes from the technique of adding two sounds together (in most cases as an effect) by older studios who used audio tape Flanges (metal or plastic tape reels). BTW...although I'm a digital cat allll the way...nothing sounds as sweet as an analog flange. You still reading this?!

Actually phasing and flanging are two different processes. Phasing is achieved through phase shifting but flanging is achieved through time delay. They sound similar and of course each of them suggests each other but the additive result in both cases is fairly different, i.e.:

"Time delay and add"



"Phase shift and add"



Not that I know anything about the subject, just repeating what I've read essentially. I have no deep understanding of the physics but I can generally hear "a" difference. I don't think phase shifting is all that common nowadays whereas chorus/delay/flanging is *everywhere*. I might be wrong.

Protocol is also right about phase cancellation, think about it this way, if one speaker cone is pushing while the other is pulling, and vice versa, what do you get? A net air movment of zero. That's a metaphorical example but you get the idea. When recording it is important to make sure things stay in phase, particularly if you are doing a stereo mic recording where it's very possible for your channels to slip out of phase. Lots of VSTs to analyze/correct phase, i.e.:



Also lots of great new tools which don't introduce phase distortions into your mix:





In the old days those "Remove vocals from records" machines sold in the back of magazines were generally using phase cancellation I believe to remove a chunk of the vocal by simply phase inverting a selected frequency range. I might be wrong but I think that was the general mode. Wavelet technology is the future of this science I believe, offering vast new accuracy. Again, I may be wrong. I believe the new sophisticated isolated sound systems in BMWs, etc. are based upon new wavelet technology form Sennheiser et al. They also still use phase cancellation though, i.e. from this article http://www.canadiandriver.com/articles/pw/05rl.htm :

Active Noise Cancellation uses two microphones in the car to detect low frequency booming from the exhaust system. The system then sends a "reverse phased audio signal" through the audio amplifier to cancel out the noise, which quietens the interior by up to 10-decibels.

As for that Lenny Kravitz I believe what I am hearing is flanger/chorus but that means nothing, I'm just speculating. Could be 100% wrong. I've read he used to use a old DOD phaser pedal but I think that was in his live rig. All the tabs for Fly Away seem to call for flanger and chorus but that means nothing either. The concencus amongst the online guitar sites seems to be flanger then chorus. Of course you would want to work out the delay times on both so that they sync up with the drums. I think I hear some Wah in there too but that may very well be a phaser. It's pretty hard to sort all that all out by ear though and I have a limited capacity for LKs music, so I'm probably doomed to never knowing for sure. Short of locating an interview with the producer that is. But even then, it's very unlikely he will reveal all the technical details behind it, usually they just give you a few vague generalities.

Anyhow I'm sure you know way more than I do about this stuff Protocol, I'm a caveman in the world of audio production. Although my mixes are getting much better, I still have miles to go...

[longedge]

Wow Corey - I've only got half an hour to spare at the moment. I'll have to come back and read this later :lol - where dooooo you find the time?

[longedge]

So what causes the constant 'slippage' between the two instances?

[Corey]

I'm not sure what's going on exactly. I simply don't have enough knowledge to diagnose this without spending some time analyzing and plotting the patterns. Whatever it is must be very simple though.