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Author Topic: HPF and Compression. Which one comes first?  (Read 1848 times)

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Offline Dede2002

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HPF and Compression. Which one comes first?
« on: November 04, 2008, 01:36:39 PM »
If I have to, should I compress first and them filter or the other way around?
Or it doesn't matter in terms of sound quality?
Thanks in advance  ;)
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Offline JD

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Re: HPF and Compression. Which one comes first?
« Reply #1 on: November 04, 2008, 01:42:42 PM »
If needed, I use the HPF first then compression. Depending on how much bass you filter out, you might need as much compression.
« Last Edit: November 04, 2008, 01:50:10 PM by JD »
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Offline Dede2002

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Re: HPF and Compression. Which one comes first?
« Reply #2 on: November 04, 2008, 01:48:42 PM »
If needed, I use the HPF first then compression. Depending on how much bass you filter out, you might need as use as much compression.

Thanks for your fast response.
But I'm not sure if I understand you.  If I am to use HPF at, say, 50hz with -5db attenuation, what Compression set up I should use?
Thanks one more time.
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Offline JD

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Re: HPF and Compression. Which one comes first?
« Reply #3 on: November 04, 2008, 01:56:35 PM »
Thanks for your fast response.
But I'm not sure if I understand you.  If I am to use HPF at, say, 50hz with -5db attenuation, what Compression set up I should use?
Thanks one more time.

Depends what you are after. Sometimes I run a little bit of compression just to squash a few of the spikes in the levels so that I can bring the overall levels up to a good listening level.

Sometimes after trimming off a little of the low end, the spikes come down enough that no compression is needed before raising the overall levels.

I use SF8 and use their compression (called Wavehammer) very sparingly. You are probably best off trying it at a couple of different levels and going with what your ears like the most.
« Last Edit: November 04, 2008, 01:59:35 PM by JD »
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easy jim

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Re: HPF and Compression. Which one comes first?
« Reply #4 on: November 04, 2008, 03:09:37 PM »
I do not think there's any 'rule' as to which should come first.  You should just be aware that both (1) a hpf will likely affect your dynamic range on a live recording since the low end typically drives the dynamics, and (2) compression will affect the final frequency balance/levels of your recording as well, with a tendency to squash those frequencies that drive the levels enough to hit the compressor's threshold and also a tendency to potentially bring out frequencies previously burried.

If I feel the raw does not need a hpf, or that the low is only a little thick but not too excessive, I will tend to apply the hpf after compression since I feel I get a more precise and better end result scooping the lows afterwards.  However, if I feel the low end is really thick and needs some serious attention, I will use EQ first and then compress.

The best way to figure out how you like it on a particular recording is to try both and then compare the results.  In a lot of cases, the 'best approach' should differ between different recordings.

Offline Dede2002

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Re: HPF and Compression. Which one comes first?
« Reply #5 on: November 04, 2008, 03:32:33 PM »
Thanks easyjim and JD. :coolguy:
+T
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Offline DSatz

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Re: HPF and Compression. Which one comes first?
« Reply #6 on: November 06, 2008, 11:58:47 PM »
You should filter first and then compress, unless you're a fan of weird dynamic effects.

Compression is gain that varies from moment to moment, depending on the level of the incoming audio signal. When the incoming signal increases in level, a compressor's gain decreases and vice versa. But think about it: The octave-to-octave balance of most music is constantly changing. So the net effect of a high-pass filter on the signal level will change as that balance shifts.

If a filter is set for unity gain and most of the energy in the program material lies above the filter's cutoff frequency, the filter will have very little effect on the signal level. But if a moment occurs when much of the signal energy falls below the filter's cutoff frequency, that same filter will reduce the overall signal level significantly. And it's the overall signal level that controls the gain of the compressor. So you should feed the compressor a signal that has already undergone whatever effect the filtering is going to have on the signal levels--in other words, you should send the compressor the filtered signal.

You wouldn't want the compressor to "duck" the level of your signal because of a strong, temporary, low-frequency sound which the filter is going to remove; that would just cause an unnecessary temporary reduction in volume when you play back the recording. That sometimes happens in TV broadcasting, and it's a very distracting effect.

--best regards
music > microphones > a recorder of some sort

Offline Kyle

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Re: HPF and Compression. Which one comes first?
« Reply #7 on: November 07, 2008, 10:19:24 AM »
DSatz,

Thank you very much for the info. I have been re-transferring some of my old recordings and applying the Waves Broadband Linear Phase EQ (for the HPF) and the L3 Ultramaximizer. The few that I have processed sound fine but it is good to know that my workflow is a bit off and why the corrections had to be made. I saved my original files (trims, fades, etc.. before heavy processing) so it is very easy to go back and make corrections. This will save me many headaches down the road. Learn something every day here.


edit: deleted some of post because I figured it out.
« Last Edit: November 08, 2008, 12:40:13 AM by Kyle »
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easy jim

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Re: HPF and Compression. Which one comes first?
« Reply #8 on: November 07, 2008, 12:46:36 PM »
Thanks for the feedback and info DSatz.  It's always an appreciated learning experience and great food for thought...

I had been going on the training and info. I'd garnered from a few live production/studio engineer friends who initially showed me how they attack post-production.  The most basic principle I gathered at those times from them was that there are no real 'rules' to one appropriate approach.

In my experience, mixing mostly from 4 track recordings (SBD + ambient mic pairs), I've found that my ears like the result better sometimes with one approach and better at other times using an opposite approach.  It seems to me that with amplified PA music and direct line feeds, vs. just an ambient source of unamplified music, there is so much variation in the sounds and frequency response based on a bunch of variables that just do not come into play at all with unamplified/acoustic music: different sound engineers' approaches to 'ringing out' or EQing for the room, different levels of dynamic processing on what's being sent through the PA, the sometimes wacky frequency response characteristics of the mics used on stage for individual channels/inputs and how the engineer EQs them, etc.  As such, my ears have often felt that pre-filtering before dyanmic processing has resulted in a 'thin' sounding final mix as compared to post-filtering (unless the frequency response is totally out of whack because of standing waves in the room that were not properly addressed in the engineer's mix, or from taking a pre EQ feed out of a SBD because the EQ is set up between the SBD and the power amp/crossovers/PA).

Regarding the "ducking" effect, which I'm aware of and understand to avoid, in my experience it comes less into play with the more conservative compression settings (low ratios of 2:1 or so with a pretty fast attack and relatively moderate release, and a threshold with an average gain reduction on peaks of ~ 6dB) I use to tame a bit of the exageration in dyanmics that results from summing the ambient and direct line sources.  I think the very aggressive, high-ratio compression settings and limiting that are typically used for TV/Radio broadcasting are not at all appropriate for post-production of matrix recordings (SBD + ambient) if the goal is to produce something that still represents the 'experience' of the show while taking advantage of having the separate and complementary sources.

After reading your post last night, I tried playing with hpf settings on both the individual tracks and the master bus (ahead of any dynamic processing) of a live reggae show I am currently mixing.  As I'm sure is obvious, getting good clean low end in the final mix is critical for a live reggae recording.  In my experimentation last night, with that particular recording, I found that I could not get a result I liked when applying a hpf in advance of dynamic processing.  Once I tamed the low end for a satisfactory sounding raw mix with EQ filtering but no dynamics processing and started applying dynamic compression, I found the low end was generally too thin and I ended up with a harsh and tinny sounding hf response from the treble instruments - particularly the cymbals and horns.  When I ran dynamic compression without any pre-filtering, and then applied a hpf to the resultant mix, I found the general frequency response to be more appropriate to the music for this recording - with the thicker, but clean sounding low end I wanted and without the harshness in the upper register (which I feel was over-accenuated when I started compressing the pre-filtered mix).  When pre-filtering, I felt I needed to re-EQ the hf range of the resultant mix post-compression to get it to sound 'right,' while a hpf after dynamic compression was sufficient for a mix that sounded 'right' to me without having to roll off and notch filter the higher frequencies to re-balance it.

I also tried pre-filtering a raw post-mix of an amplified acoustic performance, on the other hand, applying a little dynamic compression after pre-filtering.  There were times during the performance where I felt the guitar sound was too percusssive, with a lot of low end response in the 40-80Hz range whenever the player strummed or picked it hard, and I feel the engineer at the show had not appropriately filtered that guitar's channel at the SBD or in the PA mix.  In this case, my ears liked the pre-filtered result better when I tried raw mix>EQ>compression vs. raw mix>compression>EQ.

So, I still conclude that while pre-filtering before dynamic processing may be the better in general/in theory, it is not a 'rule' nor is it always the best way to go for post-mixing a 4 track ambient + SBD recording of PA amplified live music.

-some edits for spelling and clarity.
« Last Edit: November 07, 2008, 12:58:33 PM by easyjim »

Offline Kyle

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Re: HPF and Compression. Which one comes first?
« Reply #9 on: November 07, 2008, 05:08:21 PM »
aahh, getting more interesting all the time. I will conduct some experiments myself and post my results. I was using light compression as well - 3:1 ratio with about a 3dB gain reduction, so the 'ducking' it seems might be a bit of a problem (in this particular case).
« Last Edit: November 08, 2008, 12:01:11 AM by Kyle »
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Offline Dede2002

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Re: HPF and Compression. Which one comes first?
« Reply #10 on: November 08, 2008, 09:26:24 PM »
Thanks a lot DSatz, Easyjim and Kyle  :coolguy:
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