PDA

View Full Version : Audio ripped from video (avi) is lossy, right?


Damage, Inc.
2006-05-03, 11:39 AM
I was going to use my Canon Powershot SD450 to take some pictures of the Mick Thomson guitar clinic I went to, but there were no pictures allowed so I figured I just record the thing. It has a video option, so I just left it recording with the mic up (and the lens not aimed at anything really) so I could use the audio from the blank video. It records into .avi, so I ripped the audio from that (using Virtual Dub) without changing any attributes, and I was left with an 8 bit mono wav. I did an freq analysis on it (after chaning it to 16 bit) and you could think its lossless because nothing drops off, but thats just how it was ripped - basically like a transcode, right? The camera compressed it for the video when recording, so my actual source recording is lossy, correct?

I can provide a sample if needed but I don't think its really neccessary. Thanks.

brimstone
2006-05-03, 01:06 PM
At 8 bits it's not CD quality. If it has been compressed with a lossy encoder is another thing and it's hard to tell because you can put all sorts of things in a wav file.

Five
2006-05-03, 01:09 PM
do you still have the original .avi file? you need to check it with gspot to see what codec your camera uses for audio (probably lossy).

Damage, Inc.
2006-05-03, 01:53 PM
Alright well this is what GSpot told me (for the audio):

PCM Audio
11024Hz, 88kb/s, 1 Chnl

I don't know entirely what that means, but I thinking that 88 kb/s is not very good at all (if its at all related to the bittrate of mp3s).

So, then my next question would be, if I were to encode this into mp3, what would the ideal bittrate to encode it at? 88kb/s?

brimstone
2006-05-03, 02:37 PM
Your audio is uncompressed but it is recorded at a quality that is way below CD quality. That's why the bitrate is so low. If you were to extract the audio you will find that it is so small it would be no use to encode it to mp3.

Five
2006-05-03, 03:00 PM
yeah so its mono wav audio but at that sample rate the max freq is around 5.5kHz ... altho it won't have the swishy mp3 artifacts it is really bad (avg mp3 freq response goes up to 16kHz)

Damage, Inc.
2006-05-03, 09:50 PM
Alright well I explored Virtual Dub more and found a way to extract the audio exactly as it is on the file, and a three minute clips is only 1.89MB vs 7.56MB of the other wav rip, so I think this is the best possible quality version I can produce without transcoding it into uneccessary quality or file size.

Five
2006-05-03, 11:03 PM
yeah, perfect

if you need to burn it on an audio cdr you can just upsample it first