I'm not Dutch I'm afraid (although some distant relatives of mine were).
See my address in the footer...
--
Stephan M. Bernsee
http://www.dspdimension.com
Reply by Rob Vermeulen●September 25, 20042004-09-25
Al,
I assume you need a time altering algorithm that keeps the original pitch
intact (that way compressing/expanding the duration, but not the pitch)?
This is fairly easy to comprehend. I for one am definitely not a dsp guru,
but I created something similar using just the information from the DSP
dimension pages.
What I did was using the Pitch Shifter example from the page (finetuned it
/speeded it up a bit with some different FFT algorithm) to change the pitch.
Afterwards I altered the samplerate so the pitch would be back to where it
was, but now the duration has changed.
I think this should be very easy to embed in a dsp processor as the
algorithm is only based on pure basic DSP stuff (FFT -> pitch shift ->
IFFT -> Sample rate conversion).
This is a short description: At first FFT it. After the FFT you need to get
hold of the true frequencies and phases, using some windowing method (or
something like that). Than you can shift the frequencies to the left or
right (up and down actually), depending on how much you'd like to change the
duration/speed. Now go back to the bin frequency representation and do IFFT.
There you've got a neat pitch shifted piece of audio with the exact same
duration. Now change the samplerate so the original pitch comes back. And
there you go. A timestretched version of the original sound buffer.
You could play with some different types of sample-rate conversions to see
what it does to the sound quality and to the realtime aspect. I had some
good results just by linear interpolating the samples. (Not HiFi but good
enough for voices).
I suggest to use buffers of 2048 samples, FFT size also 2048 and an overlap
of 3 windows to start with. Make these parameters variable, so you can play
with them. Changing these values have effect on the quality of the result as
well as the performance. Some combinations sound good, perhaps with some
little reverb, others sound like star-wars (or as an old cassette player in
a huge bathroom). It is not true that you get better results with higher
values, just different results.
I hope this helps!
Best regards,
Rob Vermeulen
Arbor AudioCommunications
The Netherlands
"AL" <me@home.com> wrote in message
news:FtW3d.45331$U04.4095@fe1.news.blueyonder.co.uk...
> Hi,
>
> I'm a university student studying Electronics Engineering and Bournemouth
> University in England.
>
> For my final year project I need to understand how CD mixers work. I know
> they alter the sample rate to change the speed (pitch) of the track being
> output thus allowing the DJ to mix the tracks (getting the tempo's to
> match).
>
> How is this done? Are there specific DSP processors to alter the sample
> rate? Or can any standard audio DSP processor be programmed to perform
> Jerry Avins wrote:
>
>> There's a very clever (but a bit over wordy) book by Lynne Truss (she's
>> English too) called "Eats, Shoots, and Leaves" that you would do well to
>> read. There's a panda story in it.
>>
>> Jerry
>
>
> Did you just tell the panda story? :-)
>
> Regards,
> Steve
The story is (sorry, Ms. Truss) that the panda, on finishing his meal,
pulls out a gun, fires a shot into the ceiling, and starts to walk out.
The proprietor asks, "What did you do that for?" and the panda tosses
him a wildlife book saying, "I'm a panda. Read the description."
Jerry
--
... they proceeded on the sound principle that the magnitude of a lie
always contains a certain factor of credibility, ... and that therefor
... they more easily fall victim to a big lie than to a little one ...
A. H.
�����������������������������������������������������������������������
Reply by Steve Underwood●September 23, 20042004-09-23
Jerry Avins wrote:
> There's a very clever (but a bit over wordy) book by Lynne Truss (she's
> English too) called "Eats, Shoots, and Leaves" that you would do well to
> read. There's a panda story in it.
>
> Jerry
Did you just tell the panda story? :-)
Regards,
Steve
Reply by Tim Wescott●September 23, 20042004-09-23
AL wrote:
> Thank you Tim for some insight into the questions I asked.
>
>
>
> I though that this being a "public" newsgroup I would be able to post a
> seemingly innocent question without being blown away by some
> incomprehensible babble on my inconsequential misplacement of a comma.
snip
>
>
He's usually doesn't do this -- perhaps the guy who stole his first
girlfriend was named Al?
--
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
Reply by Tim Wescott●September 23, 20042004-09-23
Stephan M. Bernsee wrote:
> On 2004-09-22 00:47:55 +0200, Tim Wescott <tim@wescottnospamdesign.com>
> said:
>
>> It's not just changing the sample rate -- you need to alter the tempo
>> without throwing the music out of tune. That's going to be much more
>> sophisticated (and if you find a web site let me know).
>
>
> Tim, you do know about my DSPdimension page, don't you?
>
I've skimmed it before -- I'll have to actually read it now.
--
Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
Reply by Rob Vermeulen●September 22, 20042004-09-22
ehm, www.dspdimension.com
Sorry
"Rob Vermeulen" <rvermeulen@arbor-audio-antispam-.com> wrote in message
news:10l3382mmqq2p13@corp.supernews.com...
> Hahaha.
> "Wrong side of the bed" you said? It looks more like you've slept on a
> nail-bed ;)
>
> Ok, Al. Have you read the dspdimension pages?
> Here you can find some practical information how to do nifty time/pitch
> shifting. Perhaps you can translate some of that to suit your needs.
>
> cheers.
>
> Rob
>
>
> "Jerry Avins" <jya@ieee.org> wrote in message
> news:4150ab78$0$2665$61fed72c@news.rcn.com...
> > AL wrote:
> >
> > > Hi,
> > >
> > > I'm a university student studying Electronics Engineering and
> Bournemouth
> > > University in England.
> > >
> > > For my final year project I need to understand how CD mixers work. I
> know
> > > they alter the sample rate to change the speed (pitch) of the track
> being
> > > output thus allowing the DJ to mix the tracks (getting the tempo's to
> > > match).
> > >
> > > How is this done? Are there specific DSP processors to alter the
sample
> > > rate? Or can any standard audio DSP processor be programmed to
> > perform this
> > > task?
> > >
> > > Any help/advice/website links greatly appreciated!
> >
> >
> > AL,
> >
> > I got up on the wrong side of the bed this morning. (Actually, I just
> > finished helping someone with a Master's degree turn the paper he's
> > trying to write into comprehensible English. That's worse.) The result
> > is losing the restraint that would normally deter me from this question:
> > how does someone who has reached the senior year in a university come to
> > write "tempo's" when he means "tempos"?
> >
> > There's a very clever (but a bit over wordy) book by Lynne Truss (she's
> > English too) called "Eats, Shoots, and Leaves" that you would do well to
> > read. There's a panda story in it.
> >
> > Jerry
> > --
> > Engineering is the art of making what you want from things you can get.
> > �����������������������������������������������������������������������
> >
>
>
Reply by Rob Vermeulen●September 22, 20042004-09-22
Hahaha.
"Wrong side of the bed" you said? It looks more like you've slept on a
nail-bed ;)
Ok, Al. Have you read the dspdimension pages? (http://www.dspdimension.nl).
Here you can find some practical information how to do nifty time/pitch
shifting. Perhaps you can translate some of that to suit your needs.
cheers.
Rob
"Jerry Avins" <jya@ieee.org> wrote in message
news:4150ab78$0$2665$61fed72c@news.rcn.com...
> AL wrote:
>
> > Hi,
> >
> > I'm a university student studying Electronics Engineering and
Bournemouth
> > University in England.
> >
> > For my final year project I need to understand how CD mixers work. I
know
> > they alter the sample rate to change the speed (pitch) of the track
being
> > output thus allowing the DJ to mix the tracks (getting the tempo's to
> > match).
> >
> > How is this done? Are there specific DSP processors to alter the sample
> > rate? Or can any standard audio DSP processor be programmed to
> perform this
> > task?
> >
> > Any help/advice/website links greatly appreciated!
>
>
> AL,
>
> I got up on the wrong side of the bed this morning. (Actually, I just
> finished helping someone with a Master's degree turn the paper he's
> trying to write into comprehensible English. That's worse.) The result
> is losing the restraint that would normally deter me from this question:
> how does someone who has reached the senior year in a university come to
> write "tempo's" when he means "tempos"?
>
> There's a very clever (but a bit over wordy) book by Lynne Truss (she's
> English too) called "Eats, Shoots, and Leaves" that you would do well to
> read. There's a panda story in it.
>
> Jerry
> --
> Engineering is the art of making what you want from things you can get.
> �����������������������������������������������������������������������
>
Reply by ●September 22, 20042004-09-22
Tim Wescott <tim@wescottnospamdesign.com> writes:
> AL wrote:
> > Hi, I'm a university student studying Electronics Engineering and
> > Bournemouth University in England. For my final year project I
> > need to understand how CD mixers work. I know they alter the
> > sample rate to change the speed (pitch) of the track being output
> > thus allowing the DJ to mix the tracks (getting the tempo's to
> > match). How is this done? Are there specific DSP processors to
> > alter the sample rate? Or can any standard audio DSP processor be
> > programmed to perform this task? Any help/advice/website links
> > greatly appreciated!
> >
> It's not just changing the sample rate -- you need to alter the tempo
> without throwing the music out of tune. That's going to be much more
> sophisticated (and if you find a web site let me know).
>
> This is just the sort of thing that a standard DSP processor is made
> for, given the right software.
>
Audacity can do this on a PC hardware (not in real time on my old
Celeron box!) It's open-source so the OP should be able to glean some
info from it in theory...
Cheers,
Martin
--
martin.j.thompson@trw.com
TRW Conekt, Solihull, UK
http://www.trw.com/conekt
Reply by Stephan M. Bernsee●September 22, 20042004-09-22
On 2004-09-22 00:47:55 +0200, Tim Wescott <tim@wescottnospamdesign.com> said:
> It's not just changing the sample rate -- you need to alter the tempo
> without throwing the music out of tune. That's going to be much more
> sophisticated (and if you find a web site let me know).