Hi Mark,
Thanks for your very detailed replies, and particularly your
analysis of why some sounds respond better to speeding up/slowing
down than others.
For my music (which is mainly Pipe Organ) I find that other
programs can adjust the music by one or two semitones (a semitone is
about 6% ) before the distortion comes in. So I would not be doing
anything like 3/4 or 2/3 speed changes. One recently printed hymn
book (Together in Song - Australian Hymn Book II in 1999) has tempo
markings and the range is about 10%, which is what I find is the
variation in practice.
I can understand the reason why speeding up has less effect on the
result, as I assume the algorithm is removing information when going
faster, whereas in slowing down requires the algorithm to insert
additional detail which is must invent by some mathematical wizardry.
My requirement of a 10% speed variation range, and probably of 6%
in pitch (one semitone) is well within your 'fine' range when you
say: "I would guess unless the level of variance is between different
performers is, say more than 4/5 slower to 1.5 times faster (total
variance just short of twice the speed between the fastest and the
slowest) you should be fine."
thanks again for your help ... Clyde
On 29/02/2008, at 9:59 PM, Mark Secker wrote:
(b) Does the slowing down/speeding up introduce any noticeable
distortion.
oh yeh sorry forgot the "part the (b)" answer:
depends a couple of things:
"attack" - the speed at which a sound rises to it's peak -
anything with purely vocal work and/or bowed instruments and/or
"soft" woodwind (flute/ french horn) will sound better slowed down
and be able to be slowed down more than stuff with instruments
with a strong attack like pianos and guitars, Strong percussion
(particularly heavily reverbed rock snares) starts to sound bad
slowed down even just a little.
Quality of recording - a 98Kbps sounds bad enough at normals speed
and just gets worse and by 3/4 speed it's actually truly painful to
listen to in a very real mind jarring way
even a 320Kbps MP3 played less than 2/3rd speed is getting pretty
"crunchy" (the technical/studio term is "bit crunch" and is used as
effect by... well lets say not the kind of artists likely to
release an album of Hymns...... Tricky, Trent Reznor et. al.)
where it seems to be "stuttering" 20 or 30 times a second
(which, essentially, it is as it's chopping the audio up and
relooping small bits several dozen times a second).
Speeding audio quality up is pretty much independent of recording
quality and yu can usually push any quality recording up to twice
speed with it retaining "listenability" - past that it starts to
"gallop" as it's throwing away so much that you start to hear whole
syllables disappear from words after 2 times and by 3 times whole
words start to disappear.
I would guess unless the level of variance is between different
performers is, say more than 4/5 slower to 1.5 times faster (total
variance just short of twice the speed between the fastest and the
slowest) you should be fine for anything short of releasing it as
a CD for "listening pleasure" (though the amount of people I know
listening to MP3's ripped at sub 128Kbps seems to indicate a lot of
people have high tolerance for low fidelity audio)
--
Mark Secker Computer Support Officer
ph# 61-8-6488 1855 (ECEL) <mailto:[EMAIL PROTECTED]>
University of Western Australia - CRICOS Provider No. 00126G
~
http://www.pbase.com/marxz
"It takes an idiot to do cool things.... that's why it's cool"
- Haruhara Haruka (FLCL)
Ubi fumus, ibi fumus
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