Time Stretch Limits? -Sound Forge - PC - MAGIX Community Forums Archive

Subject:Time Stretch Limits? Posted by: Bill_Wood Date:3/31/2003 12:06:10 PM I am having trouble making small changes to the length of a sound file. I need to tweak the length of a 45 minute long file by between 0.005 seconds to 0.100 seconds. I am transferring old Quad tape recordings to digital formats using a good quality pro 1/4-track recorder to recover tracks 1 and 3 by playing back the tape forward and then flip the reel and play back again to recover tracks 2 and 4. Then I use SF6 to "reverse" the backwards file and then swap the two channels to bring it back to normal. Since there is a very small amount of slippage or tape stretch, the resulting two sets of digital sound files have a slight difference between the actual start and stop times of the music. I put a leader on both ends of the tape and use the transition between leader and tape to synchronize the start and stop times of the two sets of stereo channels. I expected to be able to use the SF6 Time Stretch function to adjust the lengths of the recorded sound files to match actual tape start and stop points. However, making very small relative changes does not seem to work as I expected it to. If I make a larger adjustment, such as 1.000 second or above it works. But down in the millisecond range it does strange things such as moving the whole file ahead or behind instead of changing the overall length of the file. I have specified the start and stop times as instructed in the On-Line help for Time Stretch. Is there a lower limit to the percentage change one can use this for? The range I need is less than 0.001% Can anyone shed any light? Bill
Subject:RE: Time Stretch Limits? Reply by: captn_spalding Date:3/31/2003 12:53:59 PM Wow! I've done a lot of thigs with old tapes and discs, but this is on i've not run into! How about stretching one 1.000 seconds and the other 1.005 seconds? I'm curious, have you had much trouble with cross talk when running the tape one way or the other? Some of those older low price four channel machines didn't have the best head/tape alignment. ..spalding
Subject:RE: Time Stretch Limits? Reply by: Chienworks Date:3/31/2003 3:01:42 PM Are you using the full version of Sound Forge or the XP/Studio version? If you've got the full version, then you're also eligible to use VegasLE, which is multitracking and non-destructive. You could load each of your tape tracks into a separate VegasLE track, then use the mouse to Ctrl-drag the end of the shorter tracks to snap to the length of the longer tracks or vice versa. The only practical limit to accuracy here is how far you can zoom in, which is in the sample range.
Subject:RE: Time Stretch Limits? Reply by: Bill_Wood Date:4/1/2003 8:02:22 AM Chien I am using the full version of SF6. And I just purchased Vegas 4 + DVD so I could master the original quad recordings in Dolby Digital 5.1. I will try Vegas 4 to see if that works better. Thanks for the tip! Bill
Subject:RE: Time Stretch Limits? Reply by: Bill_Wood Date:4/1/2003 8:09:25 AM Spalding Both the original quad recorder (Sony TC-854-4) and the 1/4-track recorder (Technics 1506) are professional machines with very good tape trasnports and the proper head spacing and alignment. There is very little cross talk from tracks 1 and 3 over to 2 and 4. It is below the ambient background noise of the concert hall in any case. Bill

Subject:Time Stretch Limits?

Posted by: Bill_Wood

Date:3/31/2003 12:06:10 PM

I am having trouble making small changes to the length of a sound file. I need to tweak the length of a 45 minute long file by between 0.005 seconds to 0.100 seconds.

I am transferring old Quad tape recordings to digital formats using a good quality pro 1/4-track recorder to recover tracks 1 and 3 by playing back the tape forward and then flip the reel and play back again to recover tracks 2 and 4. Then I use SF6 to "reverse" the backwards file and then swap the two channels to bring it back to normal.

Since there is a very small amount of slippage or tape stretch, the resulting two sets of digital sound files have a slight difference between the actual start and stop times of the music. I put a leader on both ends of the tape and use the transition between leader and tape to synchronize the start and stop times of the two sets of stereo channels.

I expected to be able to use the SF6 Time Stretch function to adjust the lengths of the recorded sound files to match actual tape start and stop points. However, making very small relative changes does not seem to work as I expected it to. If I make a larger adjustment, such as 1.000 second or above it works. But down in the millisecond range it does strange things such as moving the whole file ahead or behind instead of changing the overall length of the file.

I have specified the start and stop times as instructed in the On-Line help for Time Stretch. Is there a lower limit to the percentage change one can use this for? The range I need is less than 0.001% Can anyone shed any light?

Bill

Subject:RE: Time Stretch Limits?

Reply by: captn_spalding

Date:3/31/2003 12:53:59 PM

Wow! I've done a lot of thigs with old tapes and discs, but this is on i've not run into! How about stretching one 1.000 seconds and the other 1.005 seconds?

I'm curious, have you had much trouble with cross talk when running the tape one way or the other? Some of those older low price four channel machines didn't have the best head/tape alignment.

..spalding

Subject:RE: Time Stretch Limits?

Reply by: Chienworks

Date:3/31/2003 3:01:42 PM

Are you using the full version of Sound Forge or the XP/Studio version? If you've got the full version, then you're also eligible to use VegasLE, which is multitracking and non-destructive. You could load each of your tape tracks into a separate VegasLE track, then use the mouse to Ctrl-drag the end of the shorter tracks to snap to the length of the longer tracks or vice versa. The only practical limit to accuracy here is how far you can zoom in, which is in the sample range.

Subject:RE: Time Stretch Limits?

Reply by: Bill_Wood

Date:4/1/2003 8:02:22 AM

Chien

I am using the full version of SF6. And I just purchased Vegas 4 + DVD so I could master the original quad recordings in Dolby Digital 5.1. I will try Vegas 4 to see if that works better. Thanks for the tip!

Bill

Subject:RE: Time Stretch Limits?

Reply by: Bill_Wood

Date:4/1/2003 8:09:25 AM

Spalding

Both the original quad recorder (Sony TC-854-4) and the 1/4-track recorder (Technics 1506) are professional machines with very good tape trasnports and the proper head spacing and alignment. There is very little cross talk from tracks 1 and 3 over to 2 and 4. It is below the ambient background noise of the concert hall in any case.

Bill