[linux-audio-user] Beginner sampler questions

[Pete Bessman]

At Fri, 26 Mar 2004 14:13:25 -0500,
Chris Metzler wrote:
> 
> I could use more extended loops; but the singer provides a melody
> line, and I haven't come across an extended sample that gave me the
> impression it would work with it well.  Hence, writing my own stuff,
> but on instruments I don't play; and hence, the questions about
> one-note samples.

One-Note samples are the way things are usually done, so be reassured
that what you are trying to do is what most people try to do.

> Just to make sure I understand the last parenthetical comment -- the
> idea is that if I want to shift the sample up or down in pitch, I have
> to adjust the sample rate via interpolation in the existing samples.

You're sampler will do this for you.

> I had been thinking that this was in general a bad thing to do, and
> so if you're going to do it at all, you only want to do it over a
> few semitones at most.  But here you're saying that shifting the
> sample up in pitch is worse than shifting down in pitch.  And I'm
> guessing that the reason for that is: for a fixed sample rate,
> shifting the sample data you have up in pitch results in having
> fewer samples covering the sample data than before, which results in
> information loss.
  ^^^^^^^^^^^^^^^^

That is precisely the problem, you get "aliasing."  Check out this
page for a good and concise explanation of aliasing:

http://www.bores.com/courses/intro/basics/1_alias.htm

This doesn't happen when pitching down because you don't lose any
information.  However, if you down-pitch by, say, 10 octaves, stuff
will start to sound funny.  You can also run into other problems when
pitch-shifting; for example, formants (frequencies which are most
pronounced in a wave form) will get pitched up along with a sound,
which can have the effect of, say, making people sound like chipmunks.

All that said, I'm something of a heretic in that I don't worry much
about this.  I'm only moderately interested in using electronic
instruments to replace organic ones, and the reason most people get
their undies in a bunch over aliasing et al is because it produces
"bad" results in the sense that they are "unrealistic."  Anything
goes, and I only pointed out the 1 octave either way rule because I
got the impression you were aiming for realistic results.  However,
since you're doing a remix, I'd encourage you to eschew the rules in
favor of having fun and seeing what you can cook up.

> Actually, Specimen is the sampler I've been messing with up to this
> point.

You have good taste.

> This introduced a delay -- the sound from Specimen lagged the sound
> from all the other tracks (coming from the soundcard synth) by a
> small but noticeable bit.

I've been thinking about the potential for this to happen.  What other
instruments are you using with RoseGarden, and what buffersize are you
using for JACK?  Specimen is designed to play jitter-free with large
buffers, but a consequence of this is that all notes will lag behind
by exactly the length of the buffer.  Apps which play notes as soon as
they get them won't appear to lag at all, but once you start using
larger buffer sizes (like 2048) things will start to sound funny.

> But I haven't really cared about that so much, since once I liked
> the instrument sounds, my thought was to record the instruments
> individually into tracks in Ardour, and then adjust timing and
> relative gain there.

Eh... this is a nuisance, the necessity of which I'd like to
eliminate.

[pb]