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changing file speed with Audacity (audible quality losss ?)
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Mez
AfterDawn Addict
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22. September 2010 @ 12:05 |
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No, I am on the East Coast, but my computer must have been on your time. I posted got distracted, then when I looked at the computer I 'realized' that I hadn't posted it so I posted it again. I think that was my first double post ever. Even though I am a night person and loath the morning. For most of the jobs in my long carrier, I have needed to get up early. I am a programmer. Management usually allows programmers to have great flex hrs so, if they need you to be somewhere at a terrible time you comply with a smile if you are smart. For the last 20 yrs I have had long commutes. I live out side DC. For my last 2 jobs that totaled over 12 yrs, if I left at 8 AM I might get in at 10. If I left at 5:30 I would get in at 6:00 +/- a few minutes. I could also leave at 3 so I could get home at 3:45. If I left at 8 I would have spent 4-5 hrs on the road every day. The time cost and even the gas cost were so great, it was well worth leaving so early. Now, I usually get up early.
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Senior Member
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22. September 2010 @ 12:40 |
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I did a test comparing SF8 and Audacity to the original.
Now that I listen to it I hear a slight diminishing of the sound in each,
SF8 appears to add some artifacts while the Audacity stretch not as much so,
but it loses some of the crispness of the original.
It's generally accepted that this operation will degrade the sound slightly.
Whether you can hear it and whether you can live with it is down to the individual.
I've often done it on the sound track of downloaded avi files where I want to do
a PAL to NTSC conversion; apply a stretch of 104.27% to slow down the audio.
But in that case a loss of fidelity doesn't bother me. I just want to watch the
file and be done with it.
In this test the original file was 30.1 seconds (approx). In SF8 and Audacity
I stretched to 32.4, then 28.9, then back to original size.
http://www.mediafire.com/download.php?q1lfqkrcenvnasn
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Mez
AfterDawn Addict
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22. September 2010 @ 16:36 |
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Dave, I will take your word for it. We agree it has to alter the quality. Since I am unwilling to play with it my self, I am content with your statement. You may have sharper ears or better play-back equipment than bomber or maybe you picked a nasty piece of audio while bomber was converting something that needed work. If I did the test, I would pick something that didn't compress below 300 BR in a VBR compression. I would figure anything so intricate would expose flaws.
You could hear the diff with only 2 changes? Again, my advice was keep an original, play with a copy then make only one change to the original to play it safe. If it were me, I would leave it alone since I liked listening to the tape. I tend to be a bit sloppy with my mp3s but not archives. However, I don't even play with mp3s. I prefer the original sound since it brings back memories.
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Senior Member
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22. September 2010 @ 19:03 |
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Mez, I do not have a high-end audio PC.
I'm using basic onboard sound and $20 speakers.
But the SF8 process does cause some artifacts that are not in the original
and can quite easily be heard. IN fact, in the SF8 dialog, it actually warns
in some of the modes that artifacts may occur ! (see below)
I did 3 changes. I lengthened it, shortened it, then back to original size.
The 10mb file I linked to includes the original and the SF8 and Audacity files.
Uploaded with ImageShack.us
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Mez
AfterDawn Addict
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22. September 2010 @ 19:31 |
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Holy crap! A picture is worth a 1,00 words. Even at that low res pic you can instantly spot differences with out any blow up. My question is what are you comparing? You talk about 3 files. Original, SF and Audacity. Which are those two?
Well it doesn't take much of an ear or equipment to hear some artifacts. I have heard some that startle you.
Now I know why a friend of mine spent a grand on an audio editor.
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Senior Member
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22. September 2010 @ 19:47 |
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I showed that as an example, it's not the file I used in the test,
I just wanted to show the dialog box.
The song in the file I posted is a Radiohead track (30 second clip).
What you see in the screen shot is the left and right channel of a stereo track.
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bomber07
Suspended due to non-functional email address
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22. September 2010 @ 20:02 |
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Thanks for the additional info Mez, interesteing reading again, will check out the link.
Davexnet, thanks for running through those Speed Changes and thanks for the 3 audio samples, I'll definately put my ears to the test when I have some time this afternoon.
EDIT - I just had a spare 3-5 minutes, and listened to Davexnet's 3 samples, compared to the original file the Audacity file sounded the same to me (but I really didn't have much time at all to listen), however to my ears the Sound Forge 8 file is obviously different to the original, I can hear it quite clearly in the sound of the hi-hat within the first 5 seconds... (why is it that I can best hear these differences when listening to the hi-hat ?, I hear it as clearer&louder vs less clear&softer). Probably not a very technical way of hearing it! hahaha
This message has been edited since posting. Last time this message was edited on 22. September 2010 @ 22:00
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Mez
AfterDawn Addict
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22. September 2010 @ 20:08 |
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I guessed that you would link to the experiment image.
So what is seen here is way different because it isn't the same music but 2 channels.
You will have to help me out, I do not know how to view the image of the experiment. If I click on the link I get an upload screen, no image. If I open the link I can only see the same image and a windows update screen if I click on the arrow icon.
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Senior Member
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22. September 2010 @ 22:35 |
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Are you trying to download the audio samples?
See the mediafire link above.
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Mez
AfterDawn Addict
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22. September 2010 @ 23:33 |
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Well, Dave you got me so curious I tried it myself. I only slowed a particularly nasty piece 4% with Audacity. I am with Bomber; I couldn't tell the difference between the 2. My good speakers are starting to lose the glue. To re-glue they are only $350 a piece but if I blow them out I will never afford to get them fixed. So I converted the the lossless files to a maxed VBR and played them on my ipod. My buds are extremely high fidelity, better than my ears. However, my ears are much better than even $100 3 piece computer speaker set, which are really junk.
Maybe starting with avi files was a bad idea for an experiment that really required lossless audio. Anything less will magnify the degradation process. Bomber and I used lossless. I don't have any wave files but I have plenty of flacs.
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