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Equalization without phase distortion and non-causal effects
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golem
IsraTrance Full Member
Started Topics :
109
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Posted : Nov 11, 2008 20:49:43
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I didn't find appropriate topic for this question so I am writing it here.
I just read a course about signal processing and filtering.
I got the impression that all real-time filters need to be causal which implies that they are either linear phase filters or introduce phase distortion.
1. How are usually basic EQ or basic filters in music applications implemented? Are they IIR or FIR? Are they linear phase (constant delay) or non-linear phase filters..?
2. How about much more expensive or dedicated filters? For example Voxengo GlissEQ or mastering equalizers.
3. How complex are Sound Forqe EQ filters..? Are they zero-phase, linear-phase or introduce phase distortion..?
Usually musicians say that never use EQ to boost music but only to cut. But if you have a zero or linear phase filter, or non-linear cascaded with delay equalizer, wouldn't then the boosting keep a nice sound quality even if you boost very much (e.g. 10db) ?
Is it possible to implement such VST filter that is linear phase, with constant delay (e.g. 100 samples), but if you use the effect in Sound Forge, it will compensate for the delay and shift the processed audio 100 samples to the left automatically? |
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Kaz
IsraTrance Full Member
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2268
Posted : Nov 11, 2008 21:44
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1. Most implementations use FFT-based processing (because of the low latencies), and as such, have occasional weaknesses at certain points. There are linear phase EQs as well, and convolution based EQs (hardware emulation in most cases). Implementations differ, as does sound quality, sound coloring, and accuracy.
2. The more expensive ones (in general) give better results, but this is not always the case. Scour the internet for freeware and try and push it to the limit before buying higher end stuff. I like Voxengo GlissEQ, but apply a wide variety of them.
3. I wouldn't know about Sound Forge's EQ structure, but since it is an offline render (except for previewing), I'd assume that it just uses a complete fourier transformation. It's not like you need to do it in real-time there.
4. It's a matter of taste. Some artists that say that you should never boost a frequency - while other artists that say "hey, whatever works". I agree with the latter. If it sounds good, it is good.
5. Again, not a sound forge user, but it may have a checkbox somewhere labeled "delay compensation". If not, just delete the delay from the start of the file.
Phase distortion and the such are not quite as much an issue as you'd think. It really does come down to a matter of taste, and as such, it is recommended you gain some experience with software before buying some, and some freeware plugins are pretty badass.
If you have some cash aside for software,a Nevana 64 or 128 ($1500 and $2000 respectively) for the highest quality EQs and compressors (excluding hardware, which for this quality would cost no less, probably much more) available could be a great investment.
But start with freeware and work from there.
 http://www.myspace.com/Hooloovoo222 |
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Trip-
IsraTrance Team
Started Topics :
101
Posts :
3239
Posted : Nov 12, 2008 08:51
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Quote:
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On 2008-11-11 20:49:43, golem wrote:
Usually musicians say that never use EQ to boost music but only to cut. But if you have a zero or linear phase filter, or non-linear cascaded with delay equalizer, wouldn't then the boosting keep a nice sound quality even if you boost very much (e.g. 10db) ?
Is it possible to implement such VST filter that is linear phase, with constant delay (e.g. 100 samples), but if you use the effect in Sound Forge, it will compensate for the delay and shift the processed audio 100 samples to the left automatically?
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The EQ "rule of thumbs" do not apply just to VST software EQs, but a general EQ technique used by many engineers with different analog and digital EQs, so the question about this or that EQ is irrelevant in this issue...
Sound Forge does not apply processing in real time, therfor PDC is irrelevant too. Not only that it is possible, plugins like that exist and work just the way you describe.
Crackling universes dive into their own neverending crackle...
AgalactiA |
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-aeon-
Aeon
Started Topics :
10
Posts :
546
Posted : Nov 12, 2008 10:38
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you might have some fun with LP10, an EQ available from ddmf:
http://www.ddmf.eu/
it has fully adjustable phase response... i.e. you can change individual bands from minimum > linear > inverse minimum phase  plus it's pay-what-you-want! |
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