nacoran
1219 posts
Feb 24, 2010
4:35 PM
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I was recording in Audacity the other day, and I produced this wave that I didn't think was possible. That's not to say I played a sound that couldn't be played, just that I don't really understand what I'm looking at very well. I know bigger waves mean bigger sound, and square looking waves sound more electronic. Beyond that, I really don't know. Audacity lets you go in and visually reshape sound. What should sound look like? I don't remember any threads that dig down into the nitty-gritty of what makes a sound sound like it does, so I thought I'd start one.
Sound Clip
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LittleJoeSamson
253 posts
Feb 24, 2010
4:46 PM
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Not familiar with Audacity, but this waveform would indicate clipping, and after listening, it would seem correct.
Kinda reminds me of when someone years ago did an oscilloscope of Janis Joplin singing!
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nacoran
1221 posts
Feb 24, 2010
5:33 PM
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I've seen clipping, it usually looks flat at the top. I made this noise with sort of a lip smack on a low hole on my harmonica, without even actually taking a breath. I think it it's got something to do with one of the weighted reeds bouncing back. If I breath the sound doesn't work. It feels kind of like playing a mouth harp.
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MrVerylongusername
916 posts
Feb 24, 2010
5:45 PM
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Yeah, the smack would give the reed a sudden burst of energy to vibrate, rapidly, but with a quick decay. It sounds metallic and springy because the sound is the reed itself - not the normal vibrating air column. There's no distortion on your recording. I guess the flat topped section indicates where the lip smack was actually moving air, since there is no decay there must be some energy going in.
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MrVerylongusername
918 posts
Feb 24, 2010
5:47 PM
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I seem to recall this technique being called a kiss pop.
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Greg Heumann
319 posts
Feb 24, 2010
7:22 PM
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Yes and yes - not clipping except at 17.25 where the waveform goes beyond the border (assuming in this SW the border is max.) And the pattern that shows energy below zero and not above it? Could only be produced by artificial means. The flat tops you see at 18.75 are simply a sound sustained at the same volume for a while. In order to see clipping you need to expand the time axis considerably so you can see the individual sound waves, which will require several screenfuls per second, not several seconds per screenful as here. If they suddenly flatten out at their top and bottom, you have clipping.
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/Greg
BlowsMeAway Productions
BlueState - my band
Bluestate on iTunes
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nacoran
1222 posts
Feb 24, 2010
7:46 PM
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Gene, that's good idea!
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nacoran
1223 posts
Feb 24, 2010
7:54 PM
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Anyone know how to post a Audacity file?
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lumpy wafflesquirt
191 posts
Apr 03, 2010
11:53 AM
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I've asked my brother, he does 'stuff' with Audacity.
just remembered, I think he's away over Easter :^(
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"Come on Brackett let's get changed"
Last Edited by on Apr 04, 2010 2:20 AM
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Jim Rumbaugh
192 posts
Apr 03, 2010
12:57 PM
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I agree that it is not a typical waveform.
It could be a software glitch,
It could be a wave form created by a percusive style.
BUT
I played the sample wave form (posted above) and had my Audacity copy it. The wave I saw on my Audacity did NOT have the unussual curve.
Jim Rumbaugh
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nacoran
1557 posts
Apr 03, 2010
1:06 PM
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I can reproduce the wave form repeatedly now.
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Nate
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oldwailer
1167 posts
Apr 03, 2010
2:41 PM
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Cool! Speed it up--loop it--then play some outrageous Son of Dave type stuff over it. . .
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lumpy wafflesquirt
192 posts
Apr 06, 2010
9:40 AM
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Hi there
As my brother said, I do do development 'stuff' with Audacity, and have done some audio analysis over the years. I hope this is helpful. I tried to keep it short, but failed! :-)
I read that thread and pressed the 'download' button at http://filesocial.com/bjl8hz9 to get the mp3. It is 3.395s long and offset from the image in the post by about 14.9s.
As I'm sure you know, the MP3 format does not reproduce the sounds and waveform exactly. Better analysis could be done if it had been saved as a wav originally (perhaps).
I'm guessing that the person who recorded this is in America? (Using XP, I won't go into the XP vs vista/7 guess for now.) There is significant amount of mains hum @ 60Hz in the waveform. (Not what we get here in the UK, I'm used to 50Hz hum!) Let's deal with that first.
The hum can easily be seem in the quiet bits, say from 0.3s-0.4s. It has amplitude of about +-0.05FS or about 20% of the amplitude range. That must be audible (but not to me at the moment, since I am side-on to my speakers, the rest of the family are in bed and I left my headphones at work!). It should be reduced during the recording, but I have taken it out by 30dB using a notch filter in the EQ. http://dl.dropbox.com/u/1327769/Harmonica/trackpanel000.png
Now lets think about clipping. To 'clip' is for the signal to go beyond the bounds of something in the system, resulting in flat tops/bottoms (they are 'clipped' off). Clipping can occur at the mike, pre-amp, in a mixing desk, sound card (and there are several places within that that it can occur, I believe) or in subsequent processing. All are characterised by flat tops and bottoms but the 'flatness' and 'amplitude' can be affected by further things in the processing chain (inc. MP3). So yes, there is clipping here somewhere. Once a signal is clipped you can't recover the original as you have
lost information.
There is definitely clipping in the posted file, as can be seen in http://dl.dropbox.com/u/1327769/Harmonica/trackpanel001.png which is around 0.836-0.843s. Relatively flat tops and bottoms, possibly modified by the sound card and MP3 encoding. The bit from 0.8410-0.8415 isn't clipped. The bits that are clipped can't really be recovered.
Now let's look at the bit in question, I believe http://dl.dropbox.com/u/1327769/Harmonica/window000.png ? Gross clipping http://dl.dropbox.com/u/1327769/Harmonica/window001.png
due to the signal having an added-on wave. I've tried to separate that out as a low-frequency transient (which it is) here http://dl.dropbox.com/u/1327769/Harmonica/window004.png which might not have the correct amplitude, but is certainly representative of a 'puff' of breath on a mike (a 'kiss'?), from what I've seen before. I would recommend the following (but I'm no expert at recording)
1 Reduce the mains hum on the recording (there may be many reasons
for this)
2 Turning down the gain somewhere (?) in the system to avoid clipping
3 Filtering out stuff below 60Hz (or maybe a 100Hz cut on the mike?)
4 Do the 'kiss' by turning slightly from the mike to avoid the 'pop'.
'tis hard for me to go further without more information.
HTH
Martyn
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"Come on Brackett let's get changed"
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nacoran
1588 posts
Apr 06, 2010
11:47 AM
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Lumpy- I've got the original Audacity file, but I have no idea how to post it, since Audacity files get saves as .aup and _data. I don't know how to post it. You're right, it's related to a kiss pop, but it's a little more of tongue thing than a lip thing. Basically, it's a tongue slap draw (like an exaggerated version of how you breath in circular breathing.) It's the 1 hole draw on a low low F. After the pop it feels like it's sucking and blowing air into your mouth after each vibration of the reed. It's recorded on a really cheap microphone. (This bad boy!)
I've played a chord in a similar style for a percussive effect a little higher up on the harp. It's just struck me as a really weird looking sound.
I actually posted it over at the Audacity forum and someone suggested it looked like I'd sucked the element out of my microphone. :)
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Nate
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Last Edited by on Apr 06, 2010 11:48 AM
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Kyzer Sosa
279 posts
Apr 06, 2010
12:59 PM
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perhaps it fell victim to Musashi's blade?
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Kyzer's Travels
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