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Old October 18th, 2014, 03:04 PM   #31
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Re: Need help removing hum

Are the levels of the exported file (loudest peak is ~ -13.5 dB at ~ 3.25 seconds) the same as the levels of the original file as imported into Final Cut? If so, then I don't think the camera's limiter is involved, because the manual says it starts to limit at -6 dB and you are nowhere near that.

Did you have gain control set to manual, or to auto?

---

Also I'm a bit puzzled about what you're giving us. I see both channels are exactly the same. If I subtract the channels to produce (L-R) there is absolutely nothing there. Every sample is exactly zero. If you had recorded two stereo channels, even with the same mic connected to both, I would expect some data in (L-R) because the two preamps would be slightly different, encoding would be slightly different, etc. So I'm curious about what transforms were applied to the camera audio, before you uploaded the file to the web. At the very least you must have created a mono mix in FC, with both both output channels = (L+R), which would be different from raw data from the camera. (Or perhaps I don't fully understand what this camera does if you give it just one input channel.)

Last edited by Greg Miller; October 18th, 2014 at 09:36 PM.
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Old October 20th, 2014, 08:57 AM   #32
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Re: Need help removing hum

Quote:
Originally Posted by Greg Miller View Post
Are the levels of the exported file (loudest peak is ~ -13.5 dB at ~ 3.25 seconds) the same as the levels of the original file as imported into Final Cut? If so, then I don't think the camera's limiter is involved, because the manual says it starts to limit at -6 dB and you are nowhere near that.

Did you have gain control set to manual, or to auto?

---

Also I'm a bit puzzled about what you're giving us. I see both channels are exactly the same. If I subtract the channels to produce (L-R) there is absolutely nothing there. Every sample is exactly zero. If you had recorded two stereo channels, even with the same mic connected to both, I would expect some data in (L-R) because the two preamps would be slightly different, encoding would be slightly different, etc. So I'm curious about what transforms were applied to the camera audio, before you uploaded the file to the web. At the very least you must have created a mono mix in FC, with both both output channels = (L+R), which would be different from raw data from the camera. (Or perhaps I don't fully understand what this camera does if you give it just one input channel.)
Hi Greg,

Sorry for the mess with this file. What I uploaded was not raw. Here is the file NOT from Final Cut. All I did to this one was trimmed the original to create a sample file in Apple Logic. This was recorded to one channel on C100.
I want to know if there is anything "wrong" with this recording, and how to make it sound "better". To me it sounds distant and echoey. I don't believe peak limiter engaged during the recording.
https://www.dropbox.com/s/nv50i8ft7g...Jack2.aif?dl=0
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Old October 20th, 2014, 09:26 AM   #33
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Re: Need help removing hum

OK, this finally sounds like raw audio, so we aren't analyzing something irrelevant.

I think I still hear some of the background hum, which was predominantly at 120 Hz. Of course it's hard to tell, because you have not included any silence (i.e. no speaking) with just room tone. That is always very useful when you're trying to evaluate a recording. I would bet real money that it's still there.

I believe I hear some clothing rub at various points. Of course the talent might be moving around some props, there's no way to tell without accompanying video. If it is clothing rub, there are ways to deal with that.

It does not sound especially "distant" to me, the presence is there. But the room does sound a bit reflective and echoey. I have heard a lot worse, even on network TV. I guess it depends on the nature of the finished product. If it's more or less documentary in nature, or even educational, of someone speaking in a classroom or a big room, IMHO the sound will be characteristic of what people are seeing, so it won't be a problem. It does not reduce intelligibility. Of course if it's supposed to be a close and intimate narration, it would detract a bit.

The only ways you can reduce that echoey characteristic are either to add a lot of absorption to the room, or to use a much more directional mic (let the discussions begin!), carefully aimed at the talent. Or to do both. Your choice will be somewhat determined by that kind of visual shots you need to get.
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Old October 20th, 2014, 01:02 PM   #34
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Re: Need help removing hum

Here's a spectrogram of lower frequency region.
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Need help removing hum-spectrograph.png  
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Old October 20th, 2014, 01:48 PM   #35
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Re: Need help removing hum

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Originally Posted by Greg Miller View Post
OK, this finally sounds like raw audio, so we aren't analyzing something irrelevant.

I think I still hear some of the background hum, which was predominantly at 120 Hz. Of course it's hard to tell, because you have not included any silence (i.e. no speaking) with just room tone. That is always very useful when you're trying to evaluate a recording. I would bet real money that it's still there.

I believe I hear some clothing rub at various points. Of course the talent might be moving around some props, there's no way to tell without accompanying video. If it is clothing rub, there are ways to deal with that.

It does not sound especially "distant" to me, the presence is there. But the room does sound a bit reflective and echoey. I have heard a lot worse, even on network TV. I guess it depends on the nature of the finished product. If it's more or less documentary in nature, or even educational, of someone speaking in a classroom or a big room, IMHO the sound will be characteristic of what people are seeing, so it won't be a problem. It does not reduce intelligibility. Of course if it's supposed to be a close and intimate narration, it would detract a bit.

The only ways you can reduce that echoey characteristic are either to add a lot of absorption to the room, or to use a much more directional mic (let the discussions begin!), carefully aimed at the talent. Or to do both. Your choice will be somewhat determined by that kind of visual shots you need to get.
Greg thanks! I was wondering how I can improve this recording after the fact. I am not looking for a solution to remove clothing rub. I am looking for an overall improvement. Can I de-echo this? Does it sound like there is too much bass?
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Old October 20th, 2014, 04:07 PM   #36
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Re: Need help removing hum

Kathy,

I'm afraid I'm an "old school" guy. I think the way to have echo-free audio is not to record the echo in the first place. Fortunately I've never been up against the wall where I needed to try to remove echo after the fact. So I've never tried any echo reduction software. I did hear at least one demo that sounded somewhat convincing, but I honestly do not remember what program (or plugin) that was. The topic has been discussed here often enough, so hopefully someone else will jump in and give you a specific name. Or else use the forum search function and look for fairly recent posts, because IIRC I heard the demo fairly recently.

I've listened to this on a few different speakers, and on Sennheiser HD-280 Pro cans, which I think are reasonably accurate and flat (compared, for example, to the popular Sonys). I do not feel the file is the least bit bass heavy. Of course someone else might have a different opinion. What are you using to listen?

BTW, I do seem to hear a markedly unnatural quality to the HF portion of the audio. It really jumps out at me when I listen. It's very obvious in the ending "s" on the word "dynamics" from roughly 0:01.58 to 0:01.95 seconds (and in many later sibilants throughout this sample). You can see it in the attached spectral view, and also in the frequency scan, of this time slice. There seems to be a resonance around 5 kHz. More than that, there seems to be a significant notch from 2 kHz to 4 kHz. I don't know whether this was caused by the mic itself, mic placement (maybe reflections from a very close hard surface) or what's going on. In any case, I think I am hearing a predominant frequency around 5 kHz, rather than a nice smooth range up frequencies. To me, it sounds bad and what I hear seems to match what I see in those two displays.

Of course this could have been produced by some very badly applied EQ, but if you're sure this is a raw file, then we can rule that out. Try another mic? Clip on two mics at the same time, record one to each channel, analyze the raw stereo track?

EDIT: Are you sure this is raw? The camera literature specifies a 48 kHz sample rate. The latest file (Jack2.aif) appears to have a 44.1 kHz sample rate. If both of those statements are correct, and "Jack2.aif" is actually a converted file (not raw), then can we be sure that there wasn't some other transform that might have changed the audio quality?
Attached Thumbnails
Need help removing hum-jack2.aif-scan01.gif   Need help removing hum-jack2.aif-spectral01.gif  


Last edited by Greg Miller; October 20th, 2014 at 09:22 PM.
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Old October 20th, 2014, 10:35 PM   #37
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Re: Need help removing hum

Specifically, was the mic out in the open? Or was it buried under clothing?

Aside from that, how does this adjustment strike you?
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File Type: wav Jack2-GM01.wav (1.22 MB, 42 views)
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Old October 28th, 2014, 06:03 AM   #38
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Re: Need help removing hum

Quote:
Originally Posted by Greg Miller View Post
Kathy,

I'm afraid I'm an "old school" guy. I think the way to have echo-free audio is not to record the echo in the first place. Fortunately I've never been up against the wall where I needed to try to remove echo after the fact. So I've never tried any echo reduction software. I did hear at least one demo that sounded somewhat convincing, but I honestly do not remember what program (or plugin) that was. The topic has been discussed here often enough, so hopefully someone else will jump in and give you a specific name. Or else use the forum search function and look for fairly recent posts, because IIRC I heard the demo fairly recently.

I've listened to this on a few different speakers, and on Sennheiser HD-280 Pro cans, which I think are reasonably accurate and flat (compared, for example, to the popular Sonys). I do not feel the file is the least bit bass heavy. Of course someone else might have a different opinion. What are you using to listen?

BTW, I do seem to hear a markedly unnatural quality to the HF portion of the audio. It really jumps out at me when I listen. It's very obvious in the ending "s" on the word "dynamics" from roughly 0:01.58 to 0:01.95 seconds (and in many later sibilants throughout this sample). You can see it in the attached spectral view, and also in the frequency scan, of this time slice. There seems to be a resonance around 5 kHz. More than that, there seems to be a significant notch from 2 kHz to 4 kHz. I don't know whether this was caused by the mic itself, mic placement (maybe reflections from a very close hard surface) or what's going on. In any case, I think I am hearing a predominant frequency around 5 kHz, rather than a nice smooth range up frequencies. To me, it sounds bad and what I hear seems to match what I see in those two displays.

Of course this could have been produced by some very badly applied EQ, but if you're sure this is a raw file, then we can rule that out. Try another mic? Clip on two mics at the same time, record one to each channel, analyze the raw stereo track?

EDIT: Are you sure this is raw? The camera literature specifies a 48 kHz sample rate. The latest file (Jack2.aif) appears to have a 44.1 kHz sample rate. If both of those statements are correct, and "Jack2.aif" is actually a converted file (not raw), then can we be sure that there wasn't some other transform that might have changed the audio quality?
Hi Greg,
Sorry for a late reply. I was away. I opened the file in Apple Logic and it got converted to 44.1 kHz. I just want to trim it so I wouldn't post 2hrs of audio. I don't believe anything else was applied to the file. How can I trim and still call it RAW?
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Old October 28th, 2014, 11:06 AM   #39
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Re: Need help removing hum

Hi Kathy,

If you're sure nothing else was changed, then I guess it's close enough to call it "raw."

My concern is that there seems to be a lot of attenuation between roughly 2kHz and 4kHz. (I say that because the frequency content of the file drops off abruptly around 2kHz, but then seems to come back up around 4kHz with a bit of a peak around 5kHz.) Since the file was obviously "processed" in some way (as indicated by the change in sampling frequency), I wanted to be sure that you hadn't inadvertently applied some EQ in the process.

Of course I can't prove that those frequencies are really attenuated, compared to the actual live sound. But based on what I hear (comparing your "raw" file to my "adjusted" file), and compared to what I see in the two visual representations of the file, it certainly seems to me as if something went awry.

How does my "adjusted" sample (in my last post before this one) sound to you?

Do you have any clues as to what might have happened to that bit of the frequency spectrum? Was the mic out in the open, or was it buried under clothing? Things like that?

Any chance you have another mic of the same make/model so you could record a stereo test file, with each mic feeding a separate channel?

*** What does anyone else think of this file? How does the original file (from post #32) sound to you? Is it lacking in presence? Do you think it's weak in the 2kHz - 4kHz range, compared to lower frequencies and also compared to the peak around 5 kHz? If so, any idea what might have happened to that range of frequencies?
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Old November 13th, 2014, 10:36 AM   #40
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Re: Need help removing hum

Hi Greg,

Sorry again for such a late reply. I listened to your sample and it sounds pretty good to my ear. Since my last posting I had to redo my video removing some parts and adding others. I think I'm all set with it. After adding a music track it all sounds decent.

Thanks
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Old November 13th, 2014, 05:12 PM   #41
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Re: Need help removing hum

Hi Kathy,

Glad you got it straightened out to your satisfaction.

Did you ever have any thoughts about the seeming dip in the 2 - 4 kHz range?
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Old November 14th, 2014, 08:19 PM   #42
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Re: Need help removing hum

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Hi Kathy,

Glad you got it straightened out to your satisfaction.

Did you ever have any thoughts about the seeming dip in the 2 - 4 kHz range?
Hi Greg,

Yes, so what I was calling RAW was not really raw because it was coming from Final Cut X already edited, meaning that audio and video was cut already although no audio processing was applied obviously it was not the way it was recorded. So I think the 2-4 kHz range happened where the cuts were.
I appreciate your help. Audio is something I am really trying to improve and it's no easy.
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Old November 16th, 2014, 12:07 PM   #43
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Re: Need help removing hum

Hi Kathy,

If by "cuts" you mean "edits" (as opposed to frequency cuts due to equalization) then I don't think that's the issue. Just making a simple edit, or a fade for that matter, will not affect the frequency response at all.

Of course without some sort of comparison testing, I can't say for certain that your file had been equalized. But when I listened to it, and looked at the frequency spectrum visually, it certainly appeared that the range from about 2 kHz to 4 kHz was lower in level than the rest of the spectrum. And, to my ear at least, the "presence" was lacking, which corresponds to the above.

Maybe I'm overly analytical, but I wish I could reach some conclusion about this, because it might make things easier for you (or make your audio clearer) in the future.

If you ever have time to just record a few minutes of test file, using the lav in question and another mic which you know is good, let me know, and I'll make some suggestions.

Meanwhile, too bad NYC is 5 hours from here, or I'd be tempted to run over there for a look-see.

Cheers!
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Old November 24th, 2014, 02:26 PM   #44
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Re: Need help removing hum

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Originally Posted by Greg Miller View Post
Hi Kathy,

If by "cuts" you mean "edits" (as opposed to frequency cuts due to equalization) then I don't think that's the issue. Just making a simple edit, or a fade for that matter, will not affect the frequency response at all.

Of course without some sort of comparison testing, I can't say for certain that your file had been equalized. But when I listened to it, and looked at the frequency spectrum visually, it certainly appeared that the range from about 2 kHz to 4 kHz was lower in level than the rest of the spectrum. And, to my ear at least, the "presence" was lacking, which corresponds to the above.

Maybe I'm overly analytical, but I wish I could reach some conclusion about this, because it might make things easier for you (or make your audio clearer) in the future.

If you ever have time to just record a few minutes of test file, using the lav in question and another mic which you know is good, let me know, and I'll make some suggestions.

Meanwhile, too bad NYC is 5 hours from here, or I'd be tempted to run over there for a look-see.

Cheers!
Greg,

Thanks! How can I get you the RAW file without exporting it from somewhere? The whole RAW video is like 1hr
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Old November 25th, 2014, 10:05 AM   #45
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Re: Need help removing hum

An uncompressed 1hr. video file would be freak'n huge! That said, an uncompressed WAVE 48k/16 audio file would be about 6MB per track minute.
Some file sharing sites have don't have the usual single file size restrictions.. pCloud for instance.. and offers up-to 20GB free. About 10 gigs upon registration.
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