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View Full Version : Downsampling - how?


Discoking
2004-12-28, 09:26 AM
I have an mp2 file with following properties: 256kbps/48KHz MPEG-1, Layer II. Now I'd love to burn this to an audio cd. (Yes, this is the highest quality available. I believe it comes from digital tv.)

How do I do this and what programs do I use?

If I got this correctly, I first need to convert the mp2 file to a 48khz wav file. I can do this with Winamp DiskWriter. I'm not sure if this is a very good way though.

Then I need to downsample the 48khz file to a 44.1khz file. Now this can also be done by Winamp or even automatically by Nero. But I believe it is recommended to use more advanced programs to get a better result. I have Sound Forge. Is that ok to use? (If so, how do I have to set my parameters? What interpolation accuracy? Apply an anti-alias filter?)
I also downloaded Audacity, but I don't know how to use it in order to do the downsampling.

Thanks for any help and comments.

(I already searched this forum, but I didn't find this question. If it would have been asked before, please excuse me and tell me where.)

Five
2004-12-28, 10:48 AM
I tried changing the pitch of a 48kHz mp3 to 44.1kHz using CEP once and it sounded terrible! It really lost something in the highs. I would probably just dump it in Nero, write it to a CDRW, extract it with EAC, then try to "outperform" Nero using Soundforge. Just keep a copy of the original available for listening and try to match your new downsampled version as closely as you can to the original using eq. I can't tell you what settings to use in Soundforge 'cause I don't know that prog. Dithering might help but probably not very much. hope this helps

Discoking
2004-12-28, 02:28 PM
:\ What is dithering?

uhclem
2004-12-28, 03:15 PM
Have a look at this webpage for a commandline resampler: http://shibatch.sourceforge.net/

Five
2004-12-28, 07:27 PM
:\ What is dithering?
I just looked right now, seems dithering is only useful for lowering bitdepth. What happened is they got digital audio so noise-free that they actually had to invent something to put a little bit of noise in. Check here:
http://www.mtsu.edu/~dsmitche/rim420/reading/rim420_Dither.html

Discoking
2004-12-29, 06:28 AM
Thanks for all help and info.

Now all I wonder is if there is what program is the best to do the downsampling? Do I really have to try a couple of methods and listen? Or is e.g. Audacity or Shibatch definately better then letting Nero do the downsampling when burning?

Five
2004-12-29, 05:32 PM
I was trying out changing the sample rate using audacity but it was also changing the pitch... I'm still looking a way to do it without altering the pitch with Audacity. I would expect that CEP/Audition would be the best or equal to the best progs for the job. I'm sure Soundforge, Goldwave, Wavelab, etc. are all excellent for this purpose as well. Get access to as many different methods as you can, try it with each and carefully compare the results (including letting Nero do it) to draw a conclusion. When I get home tomorrow I'll play around with Audacity some more and see if I can find the right way to change the sample rate while maintaining pitch.

Discoking
2004-12-29, 06:09 PM
I've seen several lineages that had Sound Forge in it for downsampling, so I guess that's not a bad way.

They all used level 4/4 and an anti-alias filter.

ssamadhi97
2004-12-30, 12:06 PM
When I get home tomorrow I'll play around with Audacity some more and see if I can find the right way to change the sample rate while maintaining pitch.
Here's one way to do it:

* open file(s) with sample rate A
* set project sample rate to desired sample rate B (button in the lower left corner of the window)
* export as wav (file menu)

By the way, resample the entire show (or whatever) first when it's still one file, and then split it to tracks (using CDwave for example). If you track before resampling, prepare to end up with a metric shitload of sector boundary errors.

ssamadhi97
2004-12-30, 12:41 PM
I just looked right now, seems dithering is only useful for lowering bitdepth. What happened is they got digital audio so noise-free that they actually had to invent something to put a little bit of noise in. Check here:
http://www.mtsu.edu/~dsmitche/rim420/reading/rim420_Dither.html
No! Dithering is useful to avoid quantization distortion after performing any kind of filtering that includes multiplication operations on sample values (and this includes things like volume changes and resampling!)

(And if you didn't understand what I just said, I'd suggest reading the article you linked to ;))

Five
2004-12-30, 05:57 PM
No! Dithering is useful to avoid quantization distortion after performing any kind of filtering that includes multiplication operations on sample values (and this includes things like volume changes and resampling!)

(And if you didn't understand what I just said, I'd suggest reading the article you linked to ;))
I haven't got any experience to speak of with resampling at a new frequency, thanks for setting me straight! I really don't know all the math and science behind "triangular" and "shaping" and all that, I just do a/b tests and listen for the best result.