Why crackling sound in VirtualDub???

[dany2]

Hi!
Im want to save the audio from a divx avi film (sum of all fears), to a wav. When i do this the result i get is a wav-file witch is REALLY bad quality. The sound is crackling... I´ve tried different types of programs, virtualdub, avi2wav, goldwave... u name it!

Does anyone know how to get the sound to sound good!??

I´ve tried with other movies and they all worked well, so i´m guessing it could be something wrong with the soundformat that is in the sum of all fears-file... when i try to explore the properties of the file, it doesn´t show what format the sound is in.
is there soundformats that VirtualDub doesn´t support or what???

PLEASE HELP!!!

//Dany

[Don2050]

It may be due to the resampling of the audio from lower (22khz) to higher (44.1khz) I had this happen with me, sometimes increasing the sampling rate will amplify the flaws, or it may be resampling them to loud and cutting the peaks off the sine waves, making the audio sound distorted. Either way try and play with the audio conversion settings and see if you cannot pinpoint at what setting this happens.

If you could detail a little more about the audio and source file, ie....what the conversion settings read, where did you get the file, what kind of video file it is, etc.....

[Don2050]

ok, just re-read and saw it was a divx file.....does virtualdub list default coversion settings(no change) and how is the audio when you play the divx file normaly ?

[Don2050]

aha...or it could be what this guy said......and he sounds magnitutedes more informed than me

From Videoguy79:

[/quote]Here is my explanation of the occasional audio problems some people (including myself) see when using Tmpegenc (I can't speak for CCE users, though). In my personal experience, I only use Toolame when downsampling from 48Khz to 44.1. Tmpegenc uses the Windows sampling rate converter, which lacks anti-aliasing filters and leaves a metallic sound to voices and midrange frequencies. This effect also results in more compression artificacts due to the mp2 encoder allocating (i.e. wasting) bits to the aliased noise. (Much in the same way that a static-laden, unfiltered VHS capture also can result in wasted video bits). It's not a huge issue at 224Kbps, but gets really bad if you lower the bitrate down past 160Kbps.

Bear with me here: You see, going from 48Khz to 44.1 (or 44.1 to 32Khz) is not a mathematically simple task--you have to use a series of 200+ pole filters to accomplish it correctly. Going from 44.1Khz to 22.05 is much less complex. . .according to the Nyquist thereom, you can only represent half of the sampling frequency. For 44.1Khz, you cut off at 22.05Khz (really 20Khz w/oversampling, but that's another issue). 22.05Khz is easy--you cut the signal in half and use anti-aliasing filters to throw out everything above 11Khz. Aliasing occurs when you try to represent a higher frequency than 1/2 of the sampling frequency. Instead of this higher frequency (lets say 22.5Khz) being represented as itself, it comes back as something lower (the corresponding reciprocal harmonic) . Hence, the nasty sounds you hear in Tmpegenc. Granted, there are not many frequencies up that high, even on a DVD, but my point is that if you do a poor sampling rate conversion, your audio will sound atrocious. The encoder is not a fan of this either as it spends precious bits on the noise that could have been used for the music, etc. In a word, GIGO. When my source is already at 44.1Khz, I just use the default audio--there is not enough of a difference (to me) to warrant using toolame. Try a 30 second sample encode of material at 48Khz w/toolame and then with Tmpegenc and you'll see what I mean.

[Don2050]

DOHH ! didnt get the quote right......I will stop talking now