Re: Quality of CoreAudio SRC
Re: Quality of CoreAudio SRC
- Subject: Re: Quality of CoreAudio SRC
- From: "Mikael Hakman" <email@hidden>
- Date: Fri, 1 Feb 2008 14:07:20 +0100
- Organization: Datakonsulten AB
On February 01, 2008 12:18 AM, Rick Sustek wrote:
Regarding topic B,
The answer is simply that it is an OS for a general purpose computing
platform, and as such, supports an architecture where multiple audio
sources/applications can send data to the built-in hardware output
device, or any available hardware interface. A multiplexor. Thus,
changing the parameters on-the-fly at the bottom of a multiplexor is not
a friendly thing to be doing.
(People do actually listen to more than one source at a time! For
example, now that 'ADC on iTunes' allows us to: "Imagine watching Apple
engineers anywhere, anytime -- wherever you go", (yikes!!!) I find that
while I'm doing just that, I like to mix in a bit of heavy metal to keep
me awake! ;-) )
Please refer to my answer to Jeff regarding this aspect.
You can if you want to, write code that interfaces directly against the
HAL and essentially take over an interface. And you could create a means
to lock-out any other source from using the interface while you have it.
To be really certain of the quality, choose a certain external interface
that you trust, and recommend (or sell) it to your users. Not only would
it be more friendly to take over an interface that was dedicated to this
purpose, but you would not be subject to the varying and somewhat unknown
quality of the audio hardware that Apple builds into its machines.
Theoretically yes, in practice no. We want standard applications delivered
with the system to reproduce audio at the highest possible quality given a
particular hardware configuration, whether that configuration consists of
only Apple or also third party devices. No SRC should be done when there is
no need for it. When there is a need then of course it should be done with
the highest possible quality that the actual computing power and precision
allows.
Please do not misunderstand me. I'm not against SRC as such. On the
contrary, currently we are investigating the effect of sample rate on
quality of DAC process. This investigation includes a study of cumulative
effect of SRC up sampling and DAC. It could lead to a conclusion that the
quality loss due to SRC is outweighed by the gain in DAC due to higher
sample rate. We are using specially licensed iZotope code for this purpose
but we are at the beginning of the project.
Thanks/Mikael
_______________________________________________
Dr. Mikael Hakman
Research & Development
Datakonsulten AB, Bonadsv. 33, SE-75757 Uppsala, Sweden
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