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ZeuZ



Joined: 06/09/08
Posts: 108
Remastering old audio speeches to improve quality
      #1068068 - 28/09/13 11:20 PM
I've got channel where I am going back and trying to remaster all the old Terence Mckenna lectures so they are clearer audio. I'm using logic. So far I have just been using a denoiser to get rid of background hissing or audience ambiance. I've also been boosting and cutting EQ's of certain hums or other things. But for this audio I have the issue that the mic seems to be resonating and creating a sort of ringing noise over his vocals, would there be any way people can think of the reduce this?

Also any other techniqu8es to greatly improve the quality of old speeches would be greatly appreciated.

Thanks in advance


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Tim Gillett



Joined: 30/01/13
Posts: 633
Loc: Perth, Western Australia
Re: Remastering old audio speeches to improve quality new [Re: ZeuZ]
      #1068074 - 29/09/13 02:14 AM
Hard to know where to start here.

Was the original recording on an analog tape? If so, do you have access to that original recording? Normally getting access to that would be your first port of call.

On the YT link yes there is a furry sort of modulation distortion every time he speaks, and his sibilants are crushed and distorted. Impossible to know from here where in the recording chain this came about. If the original recording it was possibly an FM wireless mic, but then that would mean the audience also heard it like that, which wouldnt have been too pleasant for the audience at the time...

Again the best course is always to try and work from the original session tape, or perhaps as close to that first generation as possible. In cases where multiple copies have been made, and copies of copies, it can be difficult. Try and locate the best sounding copy.

What sort of tape playback machine are you using? Is it in top condition?

Cheers Tim


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Tim Gillett



Joined: 30/01/13
Posts: 633
Loc: Perth, Western Australia
Re: Remastering old audio speeches to improve quality new [Re: ZeuZ]
      #1068079 - 29/09/13 06:32 AM
I've listened again to the sample you provided, and looked at it on a Spectrum Analyzer.

Yes that nasty ringing noise seems due to two bands of modulation noise, one centred around 10khz and the other centred around 14khz. It's very clear to see on the audience applause. (If I could I'd upload the Analyzer Screenshot)

Interestingly there is virtually no actual original audio above about 6khz and what is there is very muffled. If what we are hearing is straight from an original analog cassette recording, that doesnt really make sense.

It's possible the noise has been introduced somewhere later on, perhaps in the conversion of the tape from analog to digital, perhaps via an audio compression codec, or a combination of them.

If you cant get access to a better original and redigitise better (if needed), just low pass filtering the file above about 6khz will remove a lot of that horrible noise.

Tim


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Hugh RobjohnsAdministrator
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Joined: 25/07/03
Posts: 22294
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Re: Remastering old audio speeches to improve quality new [Re: Tim Gillett]
      #1068104 - 29/09/13 11:32 AM
Quote Tim Gillett:

Yes that nasty ringing noise seems due to two bands of modulation noise, one centred around 10khz and the other centred around 14khz. It's very clear to see on the audience applause. (If I could I'd upload the Analyzer Screenshot)




You can include images by publishing the image on any publically accessible host, and then embedding a link to it in your post here using the 'IMAGE' UBB codes included in the box right below the post entry box.

However, the "furry sort of modulation distortion" you describe sounds to me very much like common or garden aliasing artefacts from a poor quality digitisation (probably with a low sample rate and inadequate anti-alias filtering) or possibly from a bad format-conversion process.

Quote:

Interestingly there is virtually no actual original audio above about 6khz and what is there is very muffled.




That being the case (I've not bothered to analyse the audio myself), steep (18dB/octave)low-pass filtering around 7kHz would probably remove most of the obvious aliasing artefacts. You could reintroduce a sense of high end with the careful use of some form of aural exciter processing, if necessary -- although I don't think it would be, actually.

H

--------------------
Technical Editor, Sound On Sound


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Tim Gillett



Joined: 30/01/13
Posts: 633
Loc: Perth, Western Australia
Re: Remastering old audio speeches to improve quality new [Re: Hugh Robjohns]
      #1068109 - 29/09/13 01:25 PM
Quote Hugh Robjohns:

Quote Tim Gillett:

Yes that nasty ringing noise seems due to two bands of modulation noise, one centred around 10khz and the other centred around 14khz. It's very clear to see on the audience applause. (If I could I'd upload the Analyzer Screenshot)




You can include images by publishing the image on any publically accessible host, and then embedding a link to it in your post here using the 'IMAGE' UBB codes included in the box right below the post entry box.

However, the "furry sort of modulation distortion" you describe sounds to me very much like common or garden aliasing artefacts from a poor quality digitisation (probably with a low sample rate and inadequate anti-alias filtering) or possibly from a bad format-conversion process.

Quote:

Interestingly there is virtually no actual original audio above about 6khz and what is there is very muffled.




That being the case (I've not bothered to analyse the audio myself), steep (18dB/octave)low-pass filtering around 7kHz would probably remove most of the obvious aliasing artefacts. You could reintroduce a sense of high end with the careful use of some form of aural exciter processing, if necessary -- although I don't think it would be, actually.

H




Thanks Hugh for the tip on uploading to a host and providing a link. I've not had to do that on other forums where within certain size limits actual files are permitted to be uploaded.

If you read carefully my second post you will see where I suggest the likelihood the modulation noises are due to poor A/D conversion and/or digital file compression issues.

So to repeat the relevent part of my second post :

"Interestingly there is virtually no actual original audio above about 6khz and what is there is very muffled. If what we are hearing is straight from an original analog cassette recording, that doesnt really make sense.
It's possible the noise has been introduced somewhere later on, perhaps in the conversion of the tape from analog to digital, perhaps via an audio compression codec, or a combination of them."

So to correct you here Hugh, if that's permitted, the essential point about the likely sources of the modulation noise I had already covered in my second post, directly above yours.

I am in agreement with you. But since I said it first, perhaps it's truer to say that in this context you are in agreement with me? Would you agree with that?

Tim


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Hugh RobjohnsAdministrator
SOS Technical Editor


Joined: 25/07/03
Posts: 22294
Loc: Worcestershire
Re: Remastering old audio speeches to improve quality new [Re: Tim Gillett]
      #1068133 - 29/09/13 06:42 PM
Quote Tim Gillett:

I've not had to do that on other forums where within certain size limits actual files are permitted to be uploaded.




We decided not to provide that facility back when we created the forums because we realised the archive storage demands would be prohibitive. It is a tad inconvenient, I agree, but when there are so many free image hosting services around these days it's not really an issue, and the majority of images people want to include are already publically viewable elsewhere anyway.

Quote:

So to correct you here Hugh, if that's permitted, the essential point about the likely sources of the modulation noise I had already covered in my second post, directly above yours.




Oh dear...

I merely wanted to point out, for the benefit of you and others, that the nasty noises in the referenced YouTube clip are almost certainly ALIASING distortions, caused by the actions I mentioned above. It is a very specific form of 'modulation noise' and well worth identifying as such in my view for the benefit of those with less experience of such problems.

H

--------------------
Technical Editor, Sound On Sound


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Tim Gillett



Joined: 30/01/13
Posts: 633
Loc: Perth, Western Australia
Re: Remastering old audio speeches to improve quality new [Re: Hugh Robjohns]
      #1068153 - 29/09/13 09:57 PM
Quote Hugh Robjohns:


Oh dear...
/
I merely wanted to point out, for the benefit of you and others, that the nasty noises in the referenced YouTube clip are almost certainly ALIASING distortions, caused by the actions I mentioned above. It is a very specific form of 'modulation noise' and well worth identifying as such in my view for the benefit of those with less experience of such problems.

H





Sure, but if you were merely adding the information that this digitally borne noise was likely aliasing artifacts, would you have begun with "However", as if disputing something?

Normally when acknowledging another's work we say something like, "yes I agree, and to expand on that ..." Why give the impression you are disputing a point already made if in fact you are not?

Tim


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Hugh RobjohnsAdministrator
SOS Technical Editor


Joined: 25/07/03
Posts: 22294
Loc: Worcestershire
Re: Remastering old audio speeches to improve quality new [Re: Tim Gillett]
      #1068156 - 29/09/13 10:55 PM
I'm not disputing anything Tim, simply adding some, hopefully helpful, technical foundations to your vague postulations...

Sorry if my use of English grammar doesn't conform to the Australian practice.

Hugh

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Tim Gillett



Joined: 30/01/13
Posts: 633
Loc: Perth, Western Australia
Re: Remastering old audio speeches to improve quality new [Re: Hugh Robjohns]
      #1068166 - 30/09/13 02:32 AM
Quote Hugh Robjohns:

I'm not disputing anything Tim, simply adding some, hopefully helpful, technical foundations to your vague postulations...

Hugh




I love it when you talk dirty...

Tim


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Tim Gillett



Joined: 30/01/13
Posts: 633
Loc: Perth, Western Australia
Re: Remastering old audio speeches to improve quality new [Re: ZeuZ]
      #1068190 - 30/09/13 09:03 AM
Here's a link to a spectrum analyzer snapshot of the file to which I referred to in an earlier post in this thread. Since it's modulation noise it only appears when there is significant audio content. With just the voice, the Spectrum Analyzer image is not very clear so I found a section of audience applause which is the closest thing to random noise in the recording and against which the modulation noise stands out starkly. The section of interest is the two peaks in the RH corner above 5khz.

Note also that on such a recording, a spectrum analysis of audience applause can be a handy tool to help identify peaks and troughs in the original system's total frequency response to the live audio. I have used this technique to help in smoothing out speech in legacy recordings where say a poor microphone with a peaky response was used.

Tim

Oops, I'm a novice to uploading images here. The image may crop out the plot above 4khz just where I wanted to show it. Never mind, just click the link and you should get the full screen shot. Thanks


http://s17.postimg.org/ufr33oj6n/YT_audio_screenshot_1_for_SOS_forum.jpg


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Hugh RobjohnsAdministrator
SOS Technical Editor


Joined: 25/07/03
Posts: 22294
Loc: Worcestershire
Re: Remastering old audio speeches to improve quality new [Re: Tim Gillett]
      #1068201 - 30/09/13 09:46 AM
Yes, that looks characteristic of alias images creeping in to the audio band, and would suggest that it has been processed with a sample rate of 11.025kHz at some point, which is a common sample rate for digital dictation recorders. It has probably then been transcoded with something nasty and lacking in adequate reconstruction and anti-alias filtering to form the YouTube file.

Your inclusion of VLF on the scale threw me for a moment -- the applause spectrum wasn't quite the shape I was expecting!

H

--------------------
Technical Editor, Sound On Sound


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Tim Gillett



Joined: 30/01/13
Posts: 633
Loc: Perth, Western Australia
Re: Remastering old audio speeches to improve quality new [Re: Hugh Robjohns]
      #1068216 - 30/09/13 11:19 AM
Quote Hugh Robjohns:



Your inclusion of VLF on the scale threw me for a moment -- the applause spectrum wasn't quite the shape I was expecting!

H




Yes my bad. After 10 years of using Wavelab's Spectrum Analyzer it was the first time ever I'd used its "snapshot" function, which I had to go looking for in the options. I then played around with the other settings trying to see if I could get the snapshot to integrate a longer time sample for a clearer view of the artifacts. Didnt notice I now had the entire left of the graph devoted to under 100hz! How very meaningful in this instance.
All back to standard now and will know next time.

Tim


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