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Turning my EQ into a compressor (or a photocopier)

 
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Foog
DC


Joined: 27 Oct 2013
Posts: 608
Location: Upper Canuckistan

PostPosted: Fri Aug 29, 2014 3:04 am    Post subject: Turning my EQ into a compressor (or a photocopier) Reply with quote

I just discovered something unnerving.

I was editing a voiceover track, thought I had finished, ran a high pass filter, realised that I had to make some minor changes, inserted the new part, and ran an HFP again on the entire track and - sssaaayy! The whole file changed visibly, not just the parts I had added. That's odd. So I ran half a dozen HPFs in a row just to see what would happen. WOAH! Did that just scythe off the top of my wave? Why yes, yes it did! When I played it back it sounded like a Panasonic AM radio, circa 1972.

I thought that an HPF was the kind of thing that you could do multiple times to the same file and it would merely do nothing on subsequent passes. But this was more like photocopying a sheet of paper, then copying the copy, then copying the copy until the resolution becomes unintellrrrarglebarglefabledrap. Any of you technically savvy folks know what's going on here?

(I was running Pro Tools and using the built in 1 channel EQ, running an HPF at around 78 hz, if it matters)
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vkuehn
DC


Joined: 24 Apr 2013
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Location: Vernon now calls Wisconsin home

PostPosted: Fri Aug 29, 2014 5:19 am    Post subject: Reply with quote

It is always an interesting learning session to take a file, make a "work copy" and then run your favorite filter or process multiple times to see what happens.

If you look closely at all the possible things you can set on your process, you may discover you have an attack time or release time or other parameter that is set too aggressively.

You can come away from such an experiment asking: If the process is THAT destructive, do I want to run it even ONCE? Your ears may hear the file after once run of the process and say: "That's great!" Some one else may listen to your recording even after only only one pass of the filter and say: "Someone sure messed up this recording!"

In audio editing and in photo processing, stirring the pot one too many times can be disastrous.
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Lee Gordon
A Zillion


Joined: 25 Jul 2008
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Location: West Hartford, CT

PostPosted: Fri Aug 29, 2014 8:29 am    Post subject: Reply with quote

Your analogy is perfect. Just like multi-generational photocopying makes each page slightly blurrier than it's predecessor AND leaves those little random dots on the page, digital processing does its processing job but also can introduce artifacts every time it does its job. If its set up properly, you won't notice after just one pass but there's usually no reason to do more passes with the same settings.

So you have now discovered that, if you use processing at all, it's better to process your corrections before you edit them into an already processed piece.
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Foog
DC


Joined: 27 Oct 2013
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Location: Upper Canuckistan

PostPosted: Fri Aug 29, 2014 10:30 am    Post subject: Reply with quote

I'm a tad embarrassed since until now I have been cavalier with my use of the HPF. Add something, change something? Run the HPF a second time. THAT behaviour ends today!

I mean, I knew that if I repeatedly apply processing that affects the "entire" signal, like compression or somesuch, then I would get artifacts and problems. But I assumed that since an HPF is just a low frequency cutoff, repeated applications would lovingly do absolutely nothing unless something with a frequency below the threshold has been added. And that it would change the audio ONLY at the points where the additions had been made! If I could mangle my photocopier analogy some more: it's as if instead of making a copy-of-a-copy-of-a-copy, I was cropping a page and recropping it, and yet the process was blurring and changing the entire look of the image on the page.

It's disconcerting Laugh

On a related note: if I incrementally "tweak" the compression of a voice a few times on a track (that is, run compression two or three times at very light settings until I am happy with the results), am I potentially mangling other, non-compression related aspects of the audio? Lately I have been putting a bit of compression on some of my P2P auditions and have run two passes instead of one sometimes when editing the audition - "first run compression was unnoticeable, let's just run that again and see how it sounds" kinda thing. Am I better off just undoing the first pass and adjusting the settings so that I can approximate the end result without doing multiple passes of the effect?
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Frank F
Fat, Old, and Sassy


Joined: 10 Nov 2004
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Location: Park City, Utah

PostPosted: Fri Aug 29, 2014 12:44 pm    Post subject: Reply with quote

I am sure you have read my opinions on processing prior to this post, but here is a summation: Do Not use processing in your files (unless requested), it cannot be undone before post.

If you must (and I still caution very limited use of processing) use processing in your files; as has been stated prior - Make This concept a habit: do your edit, save an unprocessed file, process ONCE and only once each phase of the process, save the file, and send.

If you need to do pickups later, you have the unmangled file to work with, Again follow the ONE TIME theory,

Although audio is unique in many ways, processing a long file has differnt results than processing a short file. Each has it's own distinct charchteristics; and they are noticible audibly. By creating a "one process" file, every subsequent file will be of the same color. If you change a parameter for an audio file, write the changes down and be sure to refer to the change notes later if needed.

Frank F
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Foog
DC


Joined: 27 Oct 2013
Posts: 608
Location: Upper Canuckistan

PostPosted: Fri Aug 29, 2014 3:50 pm    Post subject: Reply with quote

Frank F wrote:
I am sure you have read my opinions on processing prior to this post, but here is a summation: Do Not use processing in your files (unless requested), it cannot be undone before post.


I must say, when I noticed you saying this in an earlier thread I assumed you were erring on the side of paranoia. I am, obviously, rethinking this. (and apologies for doubting you!) Lately I have gotten in the habit of offering clients two versions of every take I send them, a raw one and one with a bit of processing. But until now (and never again) I had run an HPF on the allegedly "raw" side.

Quote:
If you must (and I still caution very limited use of processing) use processing in your files; as has been stated prior - Make This concept a habit: do your edit, save an unprocessed file, process ONCE and only once each phase of the process, save the file, and send.

If you need to do pickups later, you have the unmangled file to work with, Again follow the ONE TIME theory,
I have indeed followed that workflow, with one key (and it turns out wrongheaded) difference: my "unmangled" master had the HPF run on it because I assumed it was not subject to artifacts etc. if the process was repeated later. Oops, say I! As of this moment, I will be making that change.

Quote:
Although audio is unique in many ways, processing a long file has differnt results than processing a short file. Each has it's own distinct charchteristics; and they are noticible audibly. By creating a "one process" file, every subsequent file will be of the same color. If you change a parameter for an audio file, write the changes down and be sure to refer to the change notes later if needed.
I do that too! I use the comments section my DAW has on each track to note any processing, edit notes, and also notes I may want to pass on to the client (e.g., fast take, slow take, angry take, and so forth.) I'm glad to see that even though I was wrong about what happens with repeated applications of the HPF, I'm doing some things right.
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Frank F
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Joined: 10 Nov 2004
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PostPosted: Fri Aug 29, 2014 4:54 pm    Post subject: Reply with quote

Way to go! You are a winner! Some things right is a good step. The only way to learn is to make mistakes.

Well, I am sure you are not the only one who doubted my ramblings about audio - and many still do. I have been doing this "audio" thing for a long time, I hope I have learned a little over those years and am able to pass it on to those who will accept sage advice. Thank you.

Frank F
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vkuehn
DC


Joined: 24 Apr 2013
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Location: Vernon now calls Wisconsin home

PostPosted: Fri Aug 29, 2014 9:09 pm    Post subject: Reply with quote

I have in Internet friend who has to be the most intellectual person I know on the subject of audio. He is a consultant that I cannot afford, but when he posts, I will e there to observe what he has to say.

I remember him giving some advice one day to people who do sound in houses of worship who want to do low frequency cuts... or as we tend to say, make a High Pass Filter. I remember him specifying to use a BUTTERWORTH filter with more than 24 dB or 36 dB per octave or something in that range.

I don't know what choices Pro Tools gives you, but I just looked into my current version of Adobe Audition. And to do an HPF I can direct the software to use any of the following filter algorithms: Butterworth, Bessel, Chebychev or Elliptical. Then I can specify how steep (in dB per octave) I want the curve to be.

So using a HPF is a little bit like going to the Oncologist and having your cancer treated with Chemotherapy. You want a doctor who can calculate which Chemo is strong enough to kill the cancer without killing YOU, Or stated another way: maximum damage to the cancer while only doing a minimum amount of damage to you.

Take some white noise in a file sometime and run various equalization schemes against it. Notch out a particular frequency as though you were trying to take out the lawn blower across the street. So some low frequency cuts, do some high frequency cuts. Then display the results in a window to shows the "curve" by frequency of your audio file. You will see that some efforts to shape the tonality of your file will result in some really weird changes that are rather dramatic in some frequency range a long ways from the one you were trying to shave down or out.
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Foog
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PostPosted: Sat Aug 30, 2014 1:59 am    Post subject: Reply with quote

Anyone care to weigh in on the HPF switch on some mics? I recently acquired a CAD e100s, and I could just flip the switch if there's no downside.
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Dayo
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Joined: 10 Jan 2008
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PostPosted: Wed Sep 03, 2014 5:28 am    Post subject: Reply with quote

Foog wrote:
Anyone care to weigh in on the HPF switch on some mics? I recently acquired a CAD e100s, and I could just flip the switch if there's no downside.


It's not a mic I use but why not just try it?
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Foog
DC


Joined: 27 Oct 2013
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PostPosted: Wed Sep 03, 2014 12:29 pm    Post subject: Reply with quote

Dayo wrote:
Foog wrote:
Anyone care to weigh in on the HPF switch on some mics? I recently acquired a CAD e100s, and I could just flip the switch if there's no downside.


It's not a mic I use but why not just try it?
In lieu of any advice to the contrary I will indeed do so. But I don't entirely trust my ears. They stick out too much and I'm pretty sure I saw one of them looking at travel brochures. At any rate, I was hoping someone with more sense than I could tell me whether it was a good idea.
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Jason Huggins
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Joined: 12 Aug 2011
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PostPosted: Wed Sep 03, 2014 1:23 pm    Post subject: Reply with quote

For the HPF, I would only use it if it reduced your noise floor by enough to make a difference. I'd just look at your meters. Record some silence with the HPF off, and then flip the switch. The CAD HPF is at 80hz, but it's only a 10dB attenuation, so that won't change your sound so much that you'll lose work over it. If it makes your overall sound less noisy and evens out the waveform, I'd call it worth it. That's just me though. I'm not trying to do movie trailers with my super low ballsy voice (which I don't have). I can hear a difference with the HPF but not enough of a difference that I think my sound is bad after using it.

If it HELPS your sound then use it...if not, there is no reason to use it.
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ccpetersen
With a Side of Awesome


Joined: 19 Sep 2007
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PostPosted: Wed Sep 03, 2014 3:03 pm    Post subject: Reply with quote

I have to agree with Frank on this (and not just because he's a great guy). Wink

I learned in the studio a long time ago to be paranoid of over processing and overwriting the only copy of something. Sometimes we get files in here that are the audio equivalent of an image processed one too many times with "unsharp mask"... and no way to fix it.

So, yeah, I always make a "really raw" backup before messing with the greeblies in my software. Wink

c
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