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Topic: Skips During Real-time Recording (Read 2640 times) previous topic - next topic
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Skips During Real-time Recording

I'm converting analog music (from reel-to-reel audio tapes) into digital (AIFF files) on a 400 MHz Macintosh G4 with System 9.2.2, and occasionally (maybe once every 10 minutes, on average) there is a "skip" where there is a brief but noticable break in the continuity of the music.  For example, in a 4-beat measure, it might record "124" as if "3" wasn't in the original music, which sounds horrible!  While I was doing this conversion, nothing else was running on the computer, and I was writing the AIFF-file to an 80 GB IDE hard disk that I installed in it.  Virtual Memory was turned off, and there is 384 MB of total RAM, with about 80 MB free.  (251 MB is in a RAM-disk.)
   For these tape-to-digital conversions, I've tried two programs (N2MP3 Pro 2, and Audion 3) and it has happened with both.  (It also happened with Audion 3 while encoding into an MP3 file, LAME 3.92 at 320 kbps. Eventually I'll encode these files, either AIFF or MP3, into AAC with QuickTime 6 Pro.)
   There doesn't seem to be any pattern to the skips.  In a 100-minute tape it happened 10 times, with as many as 40 minutes of "clean skip-free music" between the times when it skipped, but sometimes several skips occurred during a single song, and sometimes just once per song followed by a long stretch of skip-free music.  ??
   I think the CPU/... is fast enough for the processing (otherwise I wouldn't be getting 40 minutes of skip-free music) but occasionally it seems to "daydream" for an instant and the incoming real-time data (from the tape) over-runs whatever the computer is doing (processing, writing to disk,...) and a skip occurs.

   What might be causing this, and how can I avoid it?
   Would changing to OS 10.2 (with multi-tasking) help? (But I wasn't running any other programs. And a local person said it might be worse with OS-X, since UNIX-based systems "wait as long as possible" to write to the hard disk, and when they eventually do write it might temporarily slow down the processing enough to cause a skip.)
   Would alloting more memory to the program help?  Or would alloting less memory (to minimize the data that "collects" between writing to disk, as described above) be better?
   There is a "disk cache" setting in the Control Panel, currently set to the default of about 8 MB; would setting this to less (or more) be helpful?  /  And I think that turning virtual memory back on would be counter-productive, but I'm not sure about how everything interacts?
  Would writing the file into a RAM-disk eliminate the skipping? (Here, file size might be limiting.  For some reason, OS 9.2.2 limits the size of a RAM-disk to 251 MB, even though [with 384 MB total] for this I would like to use more, and 251 MB is just barely big enough for a 100-minute MP3 at 320 kbps, and is much too small for a 100-minute AIFF file.)  /  By the way, why does OS-9 limit the size of a RAM-disk, and is there any way to bypass this limitation?
   Is there another program that would avoid the skips?

   There are so many factors -- CPU speed, use of RAM (by the programs and computer), writing to the hard disk, what the program is doing,... -- that I'm not sure where to start, so I'm hoping one of you knows what's wrong and how to fix it.  Thanks, in advance, for any help you're able to provide.
 
Mike

Skips During Real-time Recording

Reply #1 –
Although I'm not familiar with those two programs you're using to record,
it sounds like they're trying to flush the temporary files,
at certain time intervals, as they're recording.
That's one thing that will cause the skipping your'e hearing.
If there's a setting to "flush temporary files every ___ secs/mins"
(or something similar)...deselect it/disable it.

If that's not it......maybe somebody else can help.

Skips During Real-time Recording

Reply #2 –
Since there hasn't been much response on this list, I'll probably try a forum with specialists in how Macs work (re: operating system, processing, writing to a hard disk or ram-disk, how these might be affected by various settings,...) and maybe they'll know what's happening and why, and how to fix it.

Do any of you know what a good forum for this would be? (I know about Apple's website, and there are "system software discussions" for OS-9 and OS-X, but are there any others -- especially not requiring "usenet" software, which doesn't work well with my ISP -- that would be good for this?

PapaDoc says,
Quote
Although I'm not familiar with those two programs you're using to record,
it sounds like they're trying to flush the temporary files,
at certain time intervals, as they're recording.
That's one thing that will cause the skipping your'e hearing.
If there's a setting to "flush temporary files every ___ secs/mins"
(or something similar)...deselect it/disable it.
Quote


Unfortunately, the programs I've used (Audion 3 and N2MP3) don't allow this kind of control, although maybe other programs (AIFF-editing programs that allow line-in recording) may have this feature. If so, I'll try it.

Also, in the "AAC General" forum I'm asking about the option of doing a conversion of tape-to-MP3-to-AAC, since a tape at 320 kbps will fit into my ram-disk, but the analogous AIFF-file won't fit. The problem of pre-echo (with MP3) was mentioned, and (soon) I'll ask whether the newer versions of LAME (like the "3.92" used in Audion 3) are better at avoiding the pre-echo problems. So if you have any ideas about this, you can check this AAC-forum.

Mike

Skips During Real-time Recording

Reply #3 –
I think about the forum in which the listening test of a 24 bit recording was truncated and dithered to 16 bits, but I don't remember the name, because I formatted my hard disc in the meantime.
Anyone remembering the forum name ?