"MisterE" wrote in message
ok, from what i've gathered, usually, converting sample
rate seems to be a no-no. something you want to avoid at
all costs.
It all depends.
I've long recommended viewing sample rate conversions (SRC) as being pretty
benign. This thinking relies on my long happy experience with Adobe
Audition, which has an excellent reputation for clean SRC. Frankly, I
figured that if Adobe can sell a complete multitracking DAW program with
tons of EFX and noise reduction features for about $300, all of the more
expensive feature-rich products (like Nuendo) would be as good. Recently
somebody posted the results of some diagnostic tests of a number of DAW
programs including Audition. It turns out that it was not possible for me to
give them all the same clean bill of health. The most likely audible problem
related to spurious responses due to incomplete filtering.
Here's a rerun of that discussion:
-------------------- begin long quote ---------------
Pawel Kusmierek" wrote in message
oups.com
Carey Carlan wrote:
Audition does good SRC. It also has good dither. In fact, it has 5
different modes, 11 different noise shapes, and your choice of dither
bits. Have at and try until you find something you like.
Some SRC comparisons between various programs are available he
http://src.infinitewave.ca/
Very interesting.
Only Goldwave was bad enough in the dynamic range test to raise serious
concerns in my mind.
However there were a goodly number of well-known products with response
outside (above) the ideal range, which could IMO lead to audible problems
with aliasing:
They include:
Abletron
Anytime
Barbabatch
Bias
Cubase
Digital Performer
Goldwave
Izotope
Nuendo
Protools
Sequoia
Soundforge
Spark
Weiss (Both)
Shame shame. But, as predicted, performance of the digital filtering was
the most critical factor.
-------------------- end long quote ---------------
actually it seems like any time i've asked
about it i usually got that response without any real
explanation or what would be the best way to actually do
it if you had to. although, ive read a little and seen
mentioned somewhere that if you are going down to a
sampling rate that is exactly half of the one you started
in, that is 'ok'. because the math is more clean, as
there is no estimation required etc. something to that
extent anyway.
This is a myth. There's nothing magical about SRC involving integer
frequency ratios. AFAIK none of the SRC software out there treats them as
special cases.
There's no purpose for any SRC hardware to have special handling for integer
ratios, because integer ratios of clock frequencies pretty much don't exist
in the real world of hardware unless one clock is derived from the other.
You may think that one hardware clock is 44,100.0000000 KHz and another is
88,200.0000000 KHz but in reality they probably vary randomly by up to
0.01%. Anything but precisely exact ratios breaks any magic that might
exist. Therefore, for all practical purposes there is no magic.
now, since i learned years ago that it is best to keep my
bit depth as high as possible until the final mixdown,
then to dither and finally convert the bit depth to 16bit
if i want to do a cd, ive been working that way.
The problem here is that its pretty rare to find situations where the rule
of the weakest link does not dictate final performance. Once you downsample
to 44,100 Hz all the time and money you put into processing at higher clock
rates goes completely out the window. It's kinda like using the finest
coffee beans to make instant coffee and then peeing into the cup just to
make sure it tastes bad. Except, there's no indication that there ever was
anything wrong with 44,100 Hz sampling in the first place.
All things considered the worst thing about working at higher sample rates
is the possibility that your DAW software has a dicy SRC (see list of
suspect SRCs above) and you actually end up with something worse than what
you would have had if you started working at your final SRC and just carried
it through to the consumer.
if so,
a) would i want to convert the sample rate down on each
individual track in the mix after i have applied all of
the effects to them, before i mix them together, or would
i mix them the tracks into the final mixdown, then
convert it down? (that's maybe a stupid question)
In principle a well-written EFX would produce audibly identical results as
long as the sample rate was high enough to cover the audible range. In fact
I've seen exceptions, but they were rare.
b) would it really matter what program i used to do the
conversion if im going down exactly by half, and if so,
which programs are best for that?
Please see the long quote above.
c) what about the conversion up to a rate which is
double. say im using some samples that are 44.1 and have
lots of effects on them. if i exported that at 88.2 id
have to assume that first the sample is upsampled then
ran through the vsts at that rate then the result
exported. would that be ok (or worth doing)? or would i
only maybe gain anything from say, a softsynth which
actually creates the original sound at the higher rate?
"If its not broke, don't fix it". The purpose of an EFX is to create a
synthetic sound. Even if an EFX sounds a little different at different
sample rates, what difference does it make as long as you get a sound you
like?
i guess thats a big chunk of questions, any words of
wisdom would be appreciated.
I'd say that among the poorly-informed the so-called benefits of high sample
rates are overstated. There's no evidence that regular music like just about
all of us record is necessarily signfiicantly altered by recording at higher
sample rates than those used by the *lowly* audio CD. Many of us do
advocate 16 bits when lots of processing is involved, so that you deliver
the best possible dynamic range to the end-user who is listening to 16 bits.
Note that SACD and DVD-A, both of which bet the farm on higher sample rates
and higher dynamic range than CD, are now generally conceeded to have failed
miserably in the marketplace. Some of the people who bet their jobs on them
no longer have those jobs.