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which out of these two cables/ports is best for my miniDV camcorder?

 
 
John Navas
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      01-18-2008
On Fri, 18 Jan 2008 19:45:25 +0000 (UTC), http://www.velocityreviews.com/forums/(E-Mail Removed) (Dave
Martindale) wrote in <fmqvkl$39k$(E-Mail Removed)>:

>Even when DV cameras *do* have a USB2 port which they use to transfer
>still images at high speed to a computer, they generally just do not
>have firmware support for transferring the DV video data over USB2 -
>even though USB2 is plenty fast enough for the 25 Mbit/s DV data rate.
>
>I happen to own a Canon Optura 60, which is one of the few DV cameras
>that can transfer full video data over USB2. But it requires special
>software on the computer end, and the software only works under some
>versions of Windows, and it's not clear whether you can use the editing
>program of your choice to capture the data even then. In comparision,
>every DV camera provides a Firewire port that will do data transfer as
>well as providing some amount of remote device control, and essentially
>every editing program supports capture via Firewire. So that's the way
>to go, even with a camera that theoretically supports USB2 as well.


It's probably more the issue of Firewire being designed for high-speed
independent transfers, whereas USB is controlled by host polling. See
my prior post to this thread.

>My former computer was old enough that I had to buy a Firewire interface
>card for it. But anything you buy today will probably have a Firewire
>port or two on the motherboard.


Most laptops do not have Firewire, and many desktops don't have it
either, although it is simple and cheap to add to either. I use a
4-port PC Card with my ThinkPad that cost me all of $30 at retail.

--
Best regards,
John Navas
Panasonic DMC-FZ8 (and several others)
 
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Ilya Zakharevich
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      01-18-2008
[A complimentary Cc of this posting was sent to
John Navas
<(E-Mail Removed)>], who wrote in article <(E-Mail Removed)>:
> It's probably more the issue of Firewire being designed for high-speed
> independent transfers, whereas USB is controlled by host polling. See
> my prior post to this thread.


The conjecture I've heard on why USB2 is so much slower (in practice)
than Firewire 400 is that current drivers/adapters do not use maximal
possible buffer/window sizes.

[AFAIK, maximal practically measured transfer rate of USB2 is
33MB/sec. This (was claimed to) coincides with the maximal
theoretical transfer rate with some particlar small size of
buffer/window.]

E.g, see
http://groups.google.com/group/comp....761a99fc3c6a0d
and the thread.

Hope this helps,
Ilya
 
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Dave Martindale
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      01-19-2008
Ilya Zakharevich <(E-Mail Removed)> writes:
>[A complimentary Cc of this posting was sent to
>John Navas
><(E-Mail Removed)>], who wrote in article
><(E-Mail Removed)>:
>> It's probably more the issue of Firewire being designed for high-speed
>> independent transfers, whereas USB is controlled by host polling. See
>> my prior post to this thread.


>The conjecture I've heard on why USB2 is so much slower (in practice)
>than Firewire 400 is that current drivers/adapters do not use maximal
>possible buffer/window sizes.


>[AFAIK, maximal practically measured transfer rate of USB2 is
> 33MB/sec. This (was claimed to) coincides with the maximal
> theoretical transfer rate with some particlar small size of
> buffer/window.]


However, DV (and HDV) have a mean data rate of 25 Mbits/sec, or about 3
MBytes/sec. That's less than 10% of the measured 33 MB/sec, so
bandwidth should not be any more of a problem with USB2 than it is with
Firewire, at least on a USB2 controller that is not currently being used
by anything other than the video camera.

Dave
 
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Ilya Zakharevich
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      01-19-2008
[A complimentary Cc of this posting was sent to
Dave Martindale
<(E-Mail Removed)>], who wrote in article <fms15f$20c$(E-Mail Removed)>:
> >[AFAIK, maximal practically measured transfer rate of USB2 is
> > 33MB/sec. This (was claimed to) coincides with the maximal
> > theoretical transfer rate with some particlar small size of
> > buffer/window.]

>
> However, DV (and HDV) have a mean data rate of 25 Mbits/sec, or about 3
> MBytes/sec. That's less than 10% of the measured 33 MB/sec, so
> bandwidth should not be any more of a problem with USB2 than it is with
> Firewire, at least on a USB2 controller that is not currently being used
> by anything other than the video camera.


Sure. You could notice that this was already mentioned in the message
I replied to.

[I still hope I can spot a person who KNOWS the reasons for abysmal
performance of USB - comparing to Firewire...]

Yours,
Ilya
 
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John Navas
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      01-19-2008
On Sat, 19 Jan 2008 07:41:03 +0000 (UTC), Ilya Zakharevich
<(E-Mail Removed)> wrote in <fms9if$18im$(E-Mail Removed)>:

>[A complimentary Cc of this posting was sent to
>Dave Martindale
><(E-Mail Removed)>], who wrote in article <fms15f$20c$(E-Mail Removed)>:
>> >[AFAIK, maximal practically measured transfer rate of USB2 is
>> > 33MB/sec. This (was claimed to) coincides with the maximal
>> > theoretical transfer rate with some particlar small size of
>> > buffer/window.]

>>
>> However, DV (and HDV) have a mean data rate of 25 Mbits/sec, or about 3
>> MBytes/sec. That's less than 10% of the measured 33 MB/sec, so
>> bandwidth should not be any more of a problem with USB2 than it is with
>> Firewire, at least on a USB2 controller that is not currently being used
>> by anything other than the video camera.

>
>Sure. You could notice that this was already mentioned in the message
>I replied to.
>
>[I still hope I can spot a person who KNOWS the reasons for abysmal
>performance of USB - comparing to Firewire...]


The primary issue, as I've noted previously, is not speed, but that
Firewire is designed for continuous independent bus transfers, whereas
USB 2.0 is not, with all USB transfers controlled by the host by means
of polling. That can result in small USB transfer pauses when the host
gets busy. (Ever notice how a USB mouse pointer will sometimes move
erratically?) This is no problem with, say, a disk drive, or even a DVD
burner (given underrun protection), but when digital video is being
streamed there's often no good way to pause the stream, so when the host
gets busy, data can be lost. USB 3.0 is supposed to address this issue,
but how well it will work in practice is an open question.

--
Best regards,
John Navas
Panasonic DMC-FZ8 (and several others)
 
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Ilya Zakharevich
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      01-19-2008
[A complimentary Cc of this posting was sent to
John Navas
<(E-Mail Removed)>], who wrote in article <(E-Mail Removed)>:
> The primary issue, as I've noted previously, is not speed, but that
> Firewire is designed for continuous independent bus transfers, whereas
> USB 2.0 is not, with all USB transfers controlled by the host by means
> of polling. That can result in small USB transfer pauses when the host
> gets busy. (Ever notice how a USB mouse pointer will sometimes move
> erratically?)


No. I do not see how the effect you describe can appear; device
drivers should not be affected by the "system being busy"; an
interrupt is an interrupt is an interrupt. I may be missing more
technical details...

Yours,
Ilya
 
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Peter D
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      01-20-2008
Oh dear, where's the Geek to help you guys?

OK, I'll be the Geek.

USB 2.0 (aka USB Hi-Speed) is technically faster (480Mbps) than Firewire 400
(400Mbps).

In real life USB maximum transfers peak at about 2/3 of that speed. If you
research actual test results, you'll often see speeds max out at 1/3 of the
max of 480 Mbps. Becasue USB creates a network where every device "chats'
with the central "host" (the computer in most cases) USB 2.0 requires more
CPU prcesses than Firewire and the more peripherals that are connected and
in use the slower the USB network. So avoid situations where you are
transferring from a USB device to a USB device (USB scanner to USB external
HD, USB camcorder to USB HD). Always transfer from a single USB device to a
non-USB device if possible. And don't forget that if you have a USB keyboard
and/or mouse connected you don't have a single device on the USB bus. Evbery
time you use the mouse or keyboard, you slow the network.

Firewire comes in two flavours. The original Firewire 400/IEEE1394(a) (100,
200, or 400 Mbps) and new Firewire 800/IEEE1394b (800Mbps). There's also a
'new' 3200 Mbps standard on the way. Actual speed is much closer to
technical speed, and faster and more reliable than USB. Why? Because of the
design. As well as significant design improvements that enhance and improve
efficiency through hardware implementation and control, Firewire allows each
device to control the network and each device can "speak" directly to
another without the need for a central "host". This significantly reduces
CPU load and increases transfer rates. Real life transfer rates on Firewire
are typically 90% of the max technical speed. Even poorly
configured/implemented Firewire can run at 80% of max speed.

Why Firewire is better than USB for Video:
As well as the significant real life speed improvement of Firewire over USB,
Firewire is also much better at sustained throughput, reducing (in fact in
most cases eliminating) dropped frames commonly seen in USB transfers.

A real test you can try:
Without doing anything else on the computer, transfer 5 minutes of video
using USB 2.0 and then Firewire and count the dropped frames. Now do it
again while using the computer (surf the net, type a letter, typical use
stuff). Now compare the droppped frames. I think you'll settle on Firewire.

Some sources:
http://en.wikipedia.org/wiki/USB
http://en.wikipedia.org/wiki/FireWire


 
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Ilya Zakharevich
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      01-20-2008
[A complimentary Cc of this posting was sent to
Peter D
<please@.sk>], who wrote in article <(E-Mail Removed)>:
> In real life USB maximum transfers peak at about 2/3 of that speed. If you
> research actual test results, you'll often see speeds max out at 1/3 of the
> max of 480 Mbps. Becasue USB creates a network where every device "chats'
> with the central "host" (the computer in most cases) USB 2.0 requires more
> CPU prcesses than


.... Sorry, but the *technical contents* of this is exactly 0. If you
know WHY the throughput is not close to the theoretical maximum,
please explain. If you do not - we all ALREADY know that it is not
close to the theoretical maximum; do you see any reason to repeat this
statement again?

Thanks,
Ilya
 
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Ron Hunter
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      01-21-2008
Ilya Zakharevich wrote:
> [A complimentary Cc of this posting was sent to
> Peter D
> <please@.sk>], who wrote in article <(E-Mail Removed)>:
>> In real life USB maximum transfers peak at about 2/3 of that speed. If you
>> research actual test results, you'll often see speeds max out at 1/3 of the
>> max of 480 Mbps. Becasue USB creates a network where every device "chats'
>> with the central "host" (the computer in most cases) USB 2.0 requires more
>> CPU prcesses than

>
> ... Sorry, but the *technical contents* of this is exactly 0. If you
> know WHY the throughput is not close to the theoretical maximum,
> please explain. If you do not - we all ALREADY know that it is not
> close to the theoretical maximum; do you see any reason to repeat this
> statement again?
>
> Thanks,
> Ilya


He DID. Perhaps you could read it again.
 
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John Navas
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      01-21-2008
On Sun, 20 Jan 2008 10:10:31 -0600, "Peter D" <please@.sk> wrote in
<(E-Mail Removed)>:

>USB 2.0 (aka USB Hi-Speed) is technically faster (480Mbps) than Firewire 400
>(400Mbps).


That's raw speed, which is relatively meaningless.

>In real life USB maximum transfers peak at about 2/3 of that speed. If you
>research actual test results, you'll often see speeds max out at 1/3 of the
>max of 480 Mbps.


That actually varies widely, a function of the USB transfer type and
signaling rate, in addition to source and target device characteristics.

>Becasue USB creates a network where every device "chats'
>with the central "host" (the computer in most cases) USB 2.0 requires more
>CPU prcesses than Firewire and the more peripherals that are connected and
>in use the slower the USB network.


The "host" is both the USB host controller and the host computer.
<http://www.usb.org/developers/usbfaq/>

USB's actual throughput is a function of many variables. Typically,
the most important ones are the target device's ability to source or
sink data, the bandwidth consumption of other devices on the bus, and
the efficiency of the host's USB software stack. In some cases, PCI
latencies and processor loading can also be critical.

When more devices are active on a given USB bus, total bus throughput
tends to go up. The problem is that latency for any given device tends
to go up as well.

>So avoid situations where you are
>transferring from a USB device to a USB device (USB scanner to USB external
>HD, USB camcorder to USB HD). Always transfer from a single USB device to a
>non-USB device if possible.


Most computers have at least two USB ports, and the most important thing
is to put slow devices on one port, and fast devices on another port.

Since USB doesn't support device to device transfers, transferring data
between two devices consumes double the amount of bus bandwidth in
addition to host overhead; i.e., device 1 to host, and host to device 2,
although the impact is greatly reduced if the two devices are on
different USB ports. This usually isn't an issue with digital video.

>And don't forget that if you have a USB keyboard
>and/or mouse connected you don't have a single device on the USB bus. Evbery
>time you use the mouse or keyboard, you slow the network.


More accurately, you increase latency for other devices on the same bus
by utilizing the bus.

>Firewire comes in two flavours. The original Firewire 400/IEEE1394(a) (100,
>200, or 400 Mbps) and new Firewire 800/IEEE1394b (800Mbps). There's also a
>'new' 3200 Mbps standard on the way. Actual speed is much closer to
>technical speed, and faster and more reliable than USB. Why? Because of the
>design. As well as significant design improvements that enhance and improve
>efficiency through hardware implementation and control, Firewire allows each
>device to control the network and each device can "speak" directly to
>another without the need for a central "host". This significantly reduces
>CPU load and increases transfer rates. Real life transfer rates on Firewire
>are typically 90% of the max technical speed. Even poorly
>configured/implemented Firewire can run at 80% of max speed.


The bigger issue for video transfer is reduced latency. There's more
than enough bandwidth with either USB or Firewire.

>Why Firewire is better than USB for Video:
>As well as the significant real life speed improvement of Firewire over USB,
>Firewire is also much better at sustained throughput, reducing (in fact in
>most cases eliminating) dropped frames commonly seen in USB transfers.


That's because of bus latency.

>A real test you can try:
>Without doing anything else on the computer, transfer 5 minutes of video
>using USB 2.0 and then Firewire and count the dropped frames. Now do it
>again while using the computer (surf the net, type a letter, typical use
>stuff). Now compare the droppped frames. I think you'll settle on Firewire.
>
>Some sources:
>http://en.wikipedia.org/wiki/USB
>http://en.wikipedia.org/wiki/FireWire


--
Best regards,
John Navas
Panasonic DMC-FZ8 (and several others)
 
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