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Re: laptop audio I/O hardware



Very cool! Thanks for that technical discussion, I love learning about 
that. And I certainly can't argue technical details, I don't know 
enough about them. But I know more now.

But I can honestly state my experience, which is, and remains:

On the same system, same settings, same software: latency is different 
between the m-audio I used and the motu.

It could very well be the way the drivers are written, but whatever the 
reason. It was noticeable in my system.

> So, this was a long winded way of saying that it is difficult to
> make generalizations like "the MOTU has lower latency than the 
> M-Audio".

But it is ok to make generalizations that firewire devices are the 
same, in terms of latency? Technically, after your report, yes. Based 
on my experience, no. But I wasn't trying to make a generalization 
about all fw devices, I was answering a question using a comparison 
between devices based purely on my experience, and will try to be more 
clear in the future that it is purely my opinion/experience. So also, 
my apologies if someone felt maligned by my language if I seemed to be 
slamming someone's beloved device.

Anyway, this is a long winded way of saying I may be technically 
incorrect, but I stand by my experience.....but from now on I will say, 
"I couldn't tune the latency low enough...."

And, really, thanks Jeff, for all that great information. It helps to 
discuss from a more technical standpoint.

best regards,

Jeff



Jeff Kaiser
http://www.jeffkaisermusic.com
pfMENTUM.com  AngryVegan.com


On Jun 7, 2006, at 9:25 AM, jeff larson wrote:

>> From: Jeff Kaiser [mailto:loopersdelight@pfmentum.com]
>>
>> I created my live rig in Max/MSP. I don't know how to measure
>> latency, so I can only say I don't notice it after switching to the
> MOTU
>
> Technically it is incorrect to say that one audio interface has better
> latency than another.  Latency in a computer-based system isn't a fixed
> characteristic of a device, it is something you tune for the 
> combination
> of components in your system including the audio interface, computer,
> operating system, other attached devices, and many other tings.
>
> At a simplistic level, you can think of latency as being defined by
> two things: the size of the buffer used by the software device driver
> and the size of the buffer used by the hardware digital/audio
> converter in the interface.  You have no control over the DAC buffer
> size, but you do have control over the driver buffer size.
>
> So assuming that two devices have comparable DAC buffer sizes,
> and you set the driver buffers to be the same, the two devices
> will have exactly the same amount of latency.  One cannot be better
> than another.
>
> "But wait!" I can hear some of you say.  What about those DAC buffers?
> If one device has a smaller buffer then it has better latency right?
> Technically yes, but we're talking about extremely small buffers,
> somewhere between 5 and 100 samples.  Measurements of my sound card
> indicate that it has a buffer of around 32 samples.  I don't care how
> sensitive a musician you think you are, *you cannot hear this*.
>
> Think you can?  32 samples at 44K is about 0.64 milliseconds.  The
> speed of sound is 13.63 inches/millisecond at 75 degrees F.  So a 32
> sample buffer produces the same amount of delay as moving your head
> about 8.7 inches away from a sound source.  The difference between
> slouching over your acoustic guitar vs. sitting upright.
>
> So unless the audio interface's DAC has an extraordinarily large
> buffer, latency is determined by the device driver buffer.  As I said
> before you get to decide what this is.  You tune latency by setting
> the buffer size as low as possible without hearing artifacts that
> usually sound like clicks.  How small you can set this buffer is
> determined by a lot of things.  One of them is the quality of the
> device driver for the audio interface.
>
> If one device has a badly written driver that does not allow you to
> select small buffer sizes without hearing clicks, then you could say
> that the device "has higher latency" than another but what that
> really means is "I cannot tune latency low enough".
>
> In my limited experience with "prosumer" grade audio interfaces, the
> the device driver has never had any effect on latency.  Latency
> problems I've had have always been related to the other things running
> on the computer, and the other devices attached to it.
>
> So, this was a long winded way of saying that it is difficult to
> make generalizations like "the MOTU has lower latency than the 
> M-Audio".
> The latency you can achieve is dependent on many things in the system,
> it is rarely an intrinsic characteristic of a single device.
>
> Jeff
>