Audacity Forum

Hi everyone,
after having recorded some hours using the device "Windows DirectSound: What you hear"
I noticed that the recorded file started stuttering at exctly 6:45:47.5.
After a second try, the stuttering again started at 6:45:47.5 until the end of the file (overall length about 9.5 hours).
Any ideas how to avoid this problem?

My system:
Vista x64 SP1,
8 GB Ram,
lots of free disc space,
Soundblaster X-Fi Xtreme Music set to audio creation mode,
latest drivers installed

Thanks in advance,
Fred

leChef1001 wrote:lots of free disc space,

After 6hours 45 minutes of recording, how much is "lots"?

stevethefiddle wrote:how much is "lots"?

293 GB.

Aftrer trimming the project to the point where the stuttering starts, the project folder contains 8192 file with an overall size of 8,12 GB.
The number 8192 doesn't seem random to me. Could it be an internal limitation of the Beta?

Fred

And I presume that the 293GB is not fragmented?
When Windows runs out of contiguous disk space, the drive has to start searching for the available spaces to write the data - this reduces drive efficiency massively.

The recording length in Audacity 1.3 is unlimited, but that does not mean that you will not run into other problems. One serious issue that you have coming up is that WAV files are limited to 4GB (due to the 32bit addressing that is used in the format).

If possible, split your recording session into smaller pieces - this will also make processing, editing and generally handling the data much easier and quicker. If this is not possible, consider using a lower sample rate or lower bit depth.

I think that the maximum duration recording that has been reported on this forum is 2 months, but the user had a lot of issues to get round to achieve that and if I remember correctly, eventually wrote his own program that would write sequential files direct to disk.

Thanks for your reply.
Your presumtion is right. My drive is not noteworthy fragmented.
Besides that I think the effect of fragmentation is often overrated.
At Stereo, 44.1 kHz and 32-bit float a project file has a size of about 28 MB which is 0.46 MB/s.
A reasonably new desktop hard drive easyly reaches write speeds of more than 50 MB/s.
Even if the drive is seriously fragemented, the write speed can't drop that high.

Fred

leChef1001 wrote:Besides that I think the effect of fragmentation is often overrated.

For many applications, yes it is, but for audio (or video) it can make quite a difference.

It's not so much to do with the read/write speed, but to do with the access time (which will generally average about 8 to 10ms but may be more or less depending on how quickly the heads can move to the next location). If the drive is able to write in contiguous disk areas, then the seek time is of little relevance, but if the drive has to jump the heads all over the disk for each 1MB au file, then the extra delay may become significant.

When Audacity is so prone to fragmentation, why isn't the recordying buffered to memory before writing to the hard drive?

leChef1001 wrote:When Audacity is so prone to fragmentation, why isn't the recordying buffered to memory before writing to the hard drive?

You mean buffering to ram, then writing as one big file? There are significant performance advantages in Audacity saving lots of little data files rather than a few great big ones. For example, if you have an hour long recording and want to process just a little section in the middle, then Audacity just needs to load the relevant bits of data rather than having to read the whole file, and for making a copy for the "undo history" it only needs to make copies of the affected small data files rather than having to make a copy of the whole 600MB. So long as there is plenty of unfragmented space on the drive this system works very well. Also it is worth noting that some disk file systems handle fragmentation better than others. NTFS is a lot better than the old FAT file system, but it still has some degree of performance hit with excessive fragmentation. Ext2 is even better than NTFS and suffers virtually no slow down.

All that plus nobody wants to hear that their four hour capture crashed and there's no possibility of recovery. Millions of au files can be put back together with recovery tools.

<<<293 GB.>>>

We like two numbers when you describe the drive. Is this like a 750GB total drive or higher? I found on several machines that having massive hard drives in a machine slows things down very significantly.

Video and some audio machines arrange RAID systems for speed rather than just raw storage capacity.

The best combination, other than hard wired RAID is a 40-80 GB system or main drive C:, with a second data drive D: for the show.

Putting the OS, Program, and Data on one massive drive is asking for trouble.

Koz

stevethefiddle wrote:You mean buffering to ram, then writing as one big file?

No I mean buffering to ram and then writing a 1MB file. While writing this buffer to disk, Audacity can open a new buffer for the next chunk of data.