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How do you avoid DC offset?
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| alanzo |
I've noticed that my tracks tend to have a lot of DC Offset in them.. sometimes by as much as 12db.. I know harmonic distortion can cause this, but I have no distortion FX in my tracks..
how is DC offset caused and how can that be avoided? |
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| hey cheggy |
| Stereo delays I think can sometimes be a hidden enemy when it comes to this |
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| shockwavedj |
if you use hardware stuff (synths, FX) it's possible that your equipment would be badly coupled or near to electromagnetic sources (coils, magnets...). It can be avoided by a balanced connection. In Analog Domain 0 Hz is usually removed by a capacitor, and the most equipment doesnt respond to continuous voltage (DC).
But if you only use softsynths... some synths (specially freeware) don't care about DC. And if you enhance low freqs trough a multiband compressor or EQ, this can cause DC to appear (DC is the level at 0 Hz).
I suppose pro software will automaticly remove DC offset (even FL has an option to do it), but i'm not totally sure. I found that renowed synths like Pro-53 added DC, for example, when generating a PWM waveform.
Try with this (free):
http://www.analogx.com/contents/dow...io/dcoffset.htm
X-Hum from Waves can do DC remove
DC Killer:
http://www.tobybear.de/p_utilbag.html
Final Mix from Acuma Labs.
http://www.acumalabs.com/VST_Final_Mix.htm
But if don't want to download anything, try to remove DC with notch filters at 0 Hz (or the lowest freq you can 0-4 Hz, avoiding modifying audio freqs: 20 Hz and above).
Good luck! |
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| alanzo |
| quote: | Originally posted by shockwavedj
But if don't want to download anything, try to remove DC with notch filters at 0 Hz (or the lowest freq you can 0-4 Hz, avoiding modifying audio freqs: 20 Hz and above).
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so it's caused by in-audioable frequencies? |
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| MadThijs |
| I had some trouble with it. Removed it with a graphic eq below 30HZ rolling off. Now I put 2 eq's above my main mixer in reason and the dc offset is gone. |
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| Subtle |
| what is DC Offset :conf: |
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| shockwavedj |
DC offset is a continuous level component added to the audio signal. While you are only able to hear pressure variations (not absolute pressure, like atmospheric one) it has no sense to preserve DC on audio material. Even more, as DC consists of a displacement on the vertical axis (pressure/voltage), it can damage your speakers (thankfully speakers are prevented from this), (analog) electronical components or saturate amplifiers even though the audio level is lowest.
MadThijs, take care when using notch filters to remove DC. Filters produce phase distorsion at further frequencies than the cutoff freqs. For example, a 20 KHz lowpass filter only attenuates freqs from around 20 KHz to above, but it can produce phase distorsion till 10 KHz if the filter is not a good one. And working with low freqs, phase is a very important issue. If the audio you are working with has a lot of lo-freqs, try to use a linear phase filter/EQ.
Mathematically a DC remover is really simple:
- estimate audio mean value, DC = (A1+A2+A3+ ... +An)/n
- substract it from audio signal, A - DC |
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| RiCo |
| It's the presence of stray dc voltage or current in an ac power system. Basically, it's just an imbalance that sometimes occurs in A/D converters. :) |
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| RiCo |
I like how you added his name in the beginning of that definition.:p
| quote: | Originally posted by shockwavedj
DC offset is a continuous level component added to the audio signal. While you are only able to hear pressure variations (not absolute pressure, like atmospheric one) it has no sense to preserve DC on audio material. Even more, as DC consists of a displacement on the vertical axis (pressure/voltage), it can damage your speakers (thankfully speakers are prevented from this), (analog) electronical components or saturate amplifiers even though the audio level is lowest.
MadThijs, take care when using notch filters to remove DC. Filters produce phase distorsion at further frequencies than the cutoff freqs. For example, a 20 KHz lowpass filter only attenuates freqs from around 20 KHz to above, but it can produce phase distorsion till 10 KHz if the filter is not a good one. And working with low freqs, phase is a very important issue. If the audio you are working with has a lot of lo-freqs, try to use a linear phase filter/EQ.
Mathematically a DC remover is really simple:
- estimate audio mean value, DC = (A1+A2+A3+ ... +An)/n
- substract it from audio signal, A - DC |
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| extalin |
use a high pass filter. 20 - 30 hz
it's good to do that on a track anyway because the extremely low frequencies carry a lot of energy and limit the maximum level you can get as well as they are just unnecessary and will interfere with the 20 - 30 hz and above that you are actually interested in people hearing / feeling. |
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| BetaFactory |
| In SoundForge there is an option called "Remove very low inaudible frequencies". Is that about the same as DC offset? |
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| BelgianGuru |
In soundforge 6 : (I have DC offset when I record stuff with my 2$ microphone)
-Process
->DC OFfset
--> Remove DC offset (scan entire sound file)
Hope it helps ! |
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