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Author Topic: Inverted sweep kinda sucking it  (Read 651 times)

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funkmeister

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Inverted sweep kinda sucking it
« on: April 24, 2014, 12:08:11 AM »
So I have a huge hour long sweep from 20-20kHz and I decided to whip up a four minute inverted sweep from 20k-20Hz. The problem is that I can't hear anything on the inverted sweep until it drops under 19kHz, but with the regular upward sweep I can hear the signal all the way to the end.

I generated the sweeps in Adobe Audition CS6 at 96kHz, 24-bit at -6dB. I'm playing through my cubicle gear: NuForce Icon HD into my AKG K142HD.

So... anybody have any idea why this is happening?

I decided to do an inverted sweep because I theorized that the driver would maintain modal energies differently on an upward sweep than a downward sweep and I wanted to measure it to see if that's the case in an audible way.
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chetlanin

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Re: Inverted sweep kinda sucking it
« Reply #1 on: April 24, 2014, 03:22:10 AM »
Theory: On the way up the last frequencies are actually synthesized by the brain. They are: calculated unconsciously from statistical probabilities, so to speak (and we know that the brain has bags of comparable tricks in store). On the way down it has no idea about what to synthesize. Well, it has a wage idea about what is going on, of course,  but is probably afraid to make a fool of itself in the synchronization department.
5 to 10% seriously, Olaf.

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If 100% seriously: I have no idea.

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What is the enormously long sweep for?
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Solderdude

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Re: Inverted sweep kinda sucking it
« Reply #2 on: April 24, 2014, 05:18:38 AM »
The 'danger' of sweeps is (while looking at the frequency which you know is there) that one hears a 'pressure' above 18kHz and not so much a tone when played at high levels.

Also while we can easily detect high frequencies around 0dB (or -6 in this case) you would have to realise that in reality (in music) the highest frequencies are 20 to 40dB (or even more) lower in amplitude and these you are likely not to detect.

I have noticed similar things when sweeping and it is easy to 'cheat' when you hear a small 'tick' at the end or begin of the test indicating 'something' is there.
When doing the reverse you have to rely on your ears, when doing the normal sweep you can rely on the fact that you know there must be something there.

I don't think it is driver related but rather 'head' related.
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Use your ears to enjoy music, not as an analyser.

funkmeister

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Re: Inverted sweep kinda sucking it
« Reply #3 on: April 24, 2014, 07:03:12 PM »
I have noticed that once I'm above ~18.5kHz that the pressure effect comes in to play.

Thanks to the two responses, I found out what was going on.

@Solderdude was right. I had to turn the sound way up and then it was there. When I had a coworker play with my volume knob I could point out when it showed up.

@Chetlanin was right. I think the false hearing effect was also at play on the sweeps upward (even short sweeps) because I would 'hear' it without moving the volume knob much. BTW, I never listened to the hour long sweep. I'd just skip ahead to different parts to check out its integrity.

The reason I have such a long sweep is to get better low frequency information. The low frequency range goes by so fast on a normal sweep that measurements are a bit questionable to me. Supposedly my headphones are about -10dB at 20Hz compared to 1kHz. With the long sweep it becomes evident that it's more like -20dB or lower. I almost can't even hear it unless I really crank the volume. My bass really shows up ~34Hz.

So the long sweep has taught me a bit. I'd be interested to see how open vs. closed backs respond to the long sweep. It seems my headphones (open-back) can pop 20Hz in a burst but not really sustain it very long with the same energy.
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