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Old 2008-03-20, 16:54   Link #1
azyuma86
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Join Date: Jun 2007
High Frequency Artifacting Help

If there is a proper name for this problem I do not know it. So forgive me if my title is a little misleading.

The problem I am having trouble with deals with a high frequency ringing type sound. It is similar to the sound described in this article: http://thot.cursus.edu/en/rubrique.asp?no=24413

Or the ringing you hear in your ears after a loud noise happens near them. It plagues one of the episodes for a particular anime series I downloaded. Also, the noise only happens during spoken dialogue, not the others sounds, such as music. In the discussion thread on these forums for this particular episode, I read someone else's comment on the issue. That person mention that it is usually an issue missed by the "sound engineer" who may have an issue hearing this high frequency noise. My first thought was maybe it was a problem with the particular fansub group's work. However, I downloaded the episode from two other groups and they all had the same problem. So I'm left to assume it was a problem that happened during the RAW capture.

I figured I'd ask about this here since it seems like it would have the most knowledgeable people who may be able to help.

The two questions I have are as follows: Is there anything I can do to the file itself or some sorta filter I can download to alleviate this problem? Or is there any sorta adjustment I can make with ffdshow to correct the problem. My hearing is quite sensitive and it is rather bothersome.

Thanks for any help!
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Old 2008-03-20, 18:41   Link #2
jfs
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Wow, I just listened to the samples on that page. Are there really sounds like that throughout the files you downloaded?

I'm pretty sure it shouldn't be a production problem, at least I hope it isn't, but it might be an artifact introduced by the audio data compression.

If you use ffdshow audio for decoding audio (if you have CCCP you probably do) you can try to enable the FIR Filter function in it, it might be able to remove the sounds. You need to use the lowpass filter. (Allows low frequencies to pass and kills high frequencies.) You might need to experiment with the settings.
You can also experiment with just using the Equalizer function.
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Old 2008-03-20, 21:22   Link #3
azyuma86
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Quote:
Originally Posted by jfs View Post
Wow, I just listened to the samples on that page. Are there really sounds like that throughout the files you downloaded?

I'm pretty sure it shouldn't be a production problem, at least I hope it isn't, but it might be an artifact introduced by the audio data compression.

If you use ffdshow audio for decoding audio (if you have CCCP you probably do) you can try to enable the FIR Filter function in it, it might be able to remove the sounds. You need to use the lowpass filter. (Allows low frequencies to pass and kills high frequencies.) You might need to experiment with the settings.
You can also experiment with just using the Equalizer function.
First of all, let me thank you! Turning on the FIR filter did eliminate that noise. That was the one audio setting I didn't mess with because it seemed intimidating.

The high pitched sound in this episode isn't quite as bad as the example in the site I linked. That was more to demonstrate what it sounded like. Though it is equally as annoying!

Finally, maybe you can help me improve the use of this filter. When I use the filter the sound is eliminated but it sorta diminishes the other sounds. So what option would I mess with to get as close to the original sound while still eliminating the annoying one. The only two options it seems I can change with numerical values are "Number of taps" which is at 32 and "Frequency" which is at 6000. I'd assume frequency would be what I would want to adjust and I'd assume I'd want to raise it until just before I hear the annoying sound again. Correct me if I'm wrong!

Thanks again!
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Old 2008-03-20, 23:11   Link #4
jfs
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Yeah, having frequency at just 6000 will make the filter remove a lot of frequencies that should be kept. Try raising frequency to 12000 or higher. Actually, as high as you can go before the sound returns.

FIR is short for Finite Impulse Response, but that's really just the math behind it. I guess it could have been named something better, but well, it's not, and I'm not sure what that should be either

A mod: This thread probably belongs in tech support.
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Old 2008-03-24, 15:19   Link #5
getfresh
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When something like what jfs explained is not the case, like it is a very specific offending frequency in the middle of your frequency range, you can load audio filters in vdubmob to eq as well or you can filter the sound using a parametric EQ or graphic EQ which are found in most audio apps. I'm not gunna go into extreme depth about frequency equalization as its a very lenghty subject. But knowing the frequency ranges of what your audio is encoded to will help you alot in the future. MP3 has different ranges of frequencies for every different combo of bit depth & sample rate settings. These frequency ranges has "roll off" points where the frequencies start to get dropped off at an increasing rate. If you know the frequency range of the format you are encoding to you should always just cut all frequencies below and above a point within the "roll-off" that gives the sound less hum and buzz over all. Another thing to consider is if the original audio signal of the encoding was recorded via a digital stream, i.e. digital out from TV to digital in on computer. Sometimes this is not the case, and you have to do a "D/C remove" to the audio signal which can remove "stutter, or popping"
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Old 2008-04-03, 20:03   Link #6
SirCanealot
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You bothered fixing the problem? After I've heard this problem on so many commercial R1 DVDs?

Just amuses me is all, it's SOOO easy to fix :/
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