Re: [Linuxsampler-devel] Sampler quality comparison...

[<be...@ga...>]

Hi Mark,
A few points on the matter:

playing samples transposed by 48000/44100 = 1.088
will not cause only a pitch transpose but a shifting
in the formants too (eg pitch up a voice and you hear the mickey mouse 
effect).
So those big sample libraries that are sampled key by key (chromatically)
would technically suffer since the formant frequencies are not
like in the original, so they sound a bit worse.
Its strange that GSt does not support this since it's not so hard to do.

incorporating the feature in LS is quite easy, from a technical point
of view you just do the following.
let's make an example:
library_samplerate = 44100;
soundcard_samplerate = 48000;

when playing a note you do (for example)

root_note_frequency = 440  ( 440Hz note)
the A above middle C

I want to play the sample one octabe higher (+12 semitones),
pitch = +12
we need to calculate the speedup factor. (the position increment per sample).

so you do 
factor=2^(pitch/12) * library_samplerate / soundcard_samplerate;
if the library and soundcard sample rates are the same then the resulting
factor would be 2.0 (playing the sample one octave higher).
if the sample rates differ the factor would be adjusted for the new sample
rate.
And contrary to your belief Mark if you use decent interpolation algorithms
(like cubic and higher order ones) the resulting sound quality would not
suffer since the shape of curves are smoothly interpolated.
If you play high Hz sounds (eg 10Khz and up) of a 44.1kHz sample through
a 96KHz audio card it sounds crisper since the waves are mode of more
sample points.
But keep in mind that doubling the sample rate doubles the CPU load too
since the sampler has to process twice the amount of samples per time unit.

Don't worry LS will provide this feature.

(it does not support that feature yet so and if you play some non 44kHz GIG
files in LS they sound wrong).

PS: the advantage of using the same sample rate for the library and
for the audio out is that you can in some cases skip interpolation 
completely (especially in those chromatically sampled instruments)
which can greatly speed up the sampling routines thus leading to 
much higher polyphony (assuming that the disk can keep up :) )

cheers,
Benno
http://www.linuxsampler.org




Scrive Mark Knecht <mk...@co...>:

> 
> I agree with the both of you. Resampling is generally not the way to go. 
> I will relate one problem I ran into a while back with GSt where this 
> would have been useful.
> 
> I got a message from a guy in Europe somewhere about wanting to 
> collaborate on a tune. He sent me a Pro Tools session, both MIDI and 
> audio. I didn't notice that the session was at 48K. I do all of mine at 
> 44.1K, which is the sample rate of all GSt libraries that I own. 
> However, since I connect Pro Tools and GSt, which are on different 
> computers, through an ADAT digital sync supplied over optical cables, 
> GSt started running at 48K, the Pro Tools session speed, instead of 
> 44.1K, the sample rate of the libraries. It turns out that this 
> frequency change is almost exactly a whole note high, being just a bit 
> out of tune (try it yourself some time) so I thought he had just made a 
> mistake in his guitar tunings. It wasn't until later that I was using 
> both GSt and my guitars that I discovered the problems.
> 
> It would have been nice, in this specific case, to have a way for GST 
> (now LS) to accept a 48K clock and resample the 44.1K library into that 
> rate to keep the tuning correct. Granted it would never sound as good as 
> if the session had been done at 44.1K, but it would make LS more useful 
> to do this.
> 
> What I ended up doing was taking the MIDI tracks that went to LS and 
> transposing them by a whole step and then creating off-tuning GSt 
> session files to get the thing tuned into the audio from Pro Tools. what 
> a mess! ;-)
> 
> This is not an issue when you use and audio connection as LS will run at 
> 44.1K in stand alone mode.
> 
> - Mark
> 
> 





-------------------------------------------------
This mail sent through http://www.gardena.net