stuttering (audio gaps) and disk speed

ghenry wrote on 8/26/2001, 6:08 AM

I have a Dell Inspiron 7500 notebook with a 440 MHz Celeron processor and 128 MB RAM with a 10 GB system disk and a 20 GB firewire disk for videos (both 2 1/2" drives with 4500 revs/sec and - of course - DMA).

I'm working with PAL DV format videos.

The following applies specifically to Sonic Foundry VideoFactory:

- Despite closing all other programs and background applications, defragmenting my disks and lowering hardware graphics acceleration, despite having only one sound track: in VideoFactory the audio part of the video file 'stutters' heavily, although no such problem occurs in either Windows' Media Player, Ulead Videostudio or other media players. Can anything be done about that?

Some general questions (which may or may not be related to the above problem):

- As far as I know, video editing requires a sustained data rate of at least 12 MB/sec. Some sources speak of only 3,5 to 4 MB/sec. So what speed is actually required?

- Is there a reliable (and readily available) tool to measure the sustained data rate (of both the system and the firewire drive)?

- Some programs (like Sonic Foundry VideoFactory) recommend rotational speeds of at least 5400 revs/sec. Why should there be a minimum rotational speed as long as the sustained data rate meets requirements?

Any suggestions?
Guenther

Comments

discdude wrote on 8/26/2001, 7:35 AM

For DV editing you need a sustained transfer rate of at least 3.6 MB/sec. Why? Because that is the data rate of DV. In other words a DV video takes up 3.6 megabytes of your hard drive for every second captured. If your hard drive is not able to write that fast, you cannot capture video without dropping frames to catch up, resulting in gaps.

Different video codecs have different data rates, which probably leads to the variance in advice for HD transfer rates you observed.

Sonic Foundry and other recommend a minimum rotation speed because sustained transfer rates are a function of the rotational speed and the data density of your hard drive. Since data density figures are not marketed like rotation speed are, people recommend the rotational speed.

However, it is possible for a 4400 RPM drive to be faster than a 5400 RPM drive if the data density of a 4400 RPM drive is much higher.

BTW, a 7200 RPM hard drive is usually recommend for DV editing.

Notebook drives are built for energy efficiency and not performance so some notebook drives may not be fast enough for DV editing. I think pretty much every desktop HD available today can do DV editing.

I hope this helps (I know I threw a lot of technical details your way).

ghenry wrote on 8/27/2001, 10:03 AM

Thanks a lot for your answer (which was by no means too technical). Your answer confirms what I thought - the rotational speed is of importance only insofar as it contributes to the sustained data rate.

No - the differing advice as to the minimum sustained data rate does not (as far as I can see) have anything to with codecs; there must be another explanation.

Same question as in my first email: do you know of any reliable tool with which to measure the SUSTAINED data rate?

Thanks
Guenther

Jdodge wrote on 8/29/2001, 4:05 PM

Hello, and thanks for adding to the forum.

Are you are experiencing these 'audio gaps' during playback from the timeline, post video capture, while working on the project? When you are capturing the video? Or are the glitches showing up after you have rendered the project and have re-opened the rendered file into VideoFactory for playback?

ghenry wrote on 9/10/2001, 7:14 AM

Thanks for your answer - and sorry for my replying so late; I was away for a couple of weeks.

The audio gaps (or 'stuttering' or 'choppiness') occur right while playing a newly inserted file from the timeline. The dv video file (AVI) was captured (and edited) earlier with Ulead VideoStudio.

Regards
Günther

SonyEPM wrote on 9/10/2001, 8:55 AM

try rendering a section of the Ulead-captured file (30 seconds to be safe), then reload that in VideoFactory. Do you still get the stuttering?