FPGA Central

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 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.) What it
boils down to 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.

Jerry
--
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

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.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

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.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Jerry Avins wrote:

(snip)

> 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.

Any relation to the second amendment, "right to arm bears"?

-- glen

Jerry Avins <jya@ieee.org> 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!
>
>
> 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.

And when's the last time you saw someone struggling with "who/whom"? We
just don't even try any more.
--
Randy Yates
Sony Ericsson Mobile Communications
Research Triangle Park, NC, USA
randy.yates@sonyericsson.com, 919-472-1124

Randy Yates wrote:

> Jerry Avins <jya@ieee.org> 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!
>>
>>
>>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.
>
>
> And when's the last time you saw someone struggling with "who/whom"? We
> just don't even try any more.

Whom says? ;^)

Jerry
--
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

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.



I admit my post was made in some haste; I am excited about a new project I
hope to start soon therefore did not have the foresight to gather the Oxford
English dictionary and Roget's thesaurus and ready myself properly for the
almighty task of putting together a request on an internet newsgroup.



So am I to gather from Mr Jerry Avins' comments that I am in fact not
welcome here? Is this some sort of clique that only seasoned professional
electronic engineers with an exquisite command of the English language can
attend and pass comment and judgment upon the naive wanderer who may
actually just only require some gentle advice? A prod or push in the right
direction so to speak?



If my question was not an acceptable one please someone point out why? I was
under the impression if you were polite enough and I have no reason to
suspect my post was not, some advice could be asked of the high and mighty
knowledgeable of the internet brethren.



Anyway it's now approaching 3AM in London, so I must close this case. I
apologise for any inconvenience caused as only a misplaced comma can.



AL.



"Tim Wescott" <tim@wescottnospamdesign.com> wrote in message
news:10l1bseqqs6s8b0@corp.supernews.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!
> >
> >
> 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.
>
> --
>
> Tim Wescott
> Wescott Design Services
> http://www.wescottdesign.com

If you are thinking of a hardware solution like building a board for
your project, i am pretty sure there are codecs (alternatively ADC and
DAC chips) that support sample rate conversion. Check out codecs from
cirrus logic. You do not need a DSP in this case because,
simplistically speaking, you are not doing any kind of processing on
the data coming from the ADC or codec.

I am new to this list and this is infact my first attempt at answering
queries. So please cross check with somebody more knowledgeable.

Thanks.

-vj



"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 this
> task?
>
> Any help/advice/website links greatly appreciated!

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.

It was an apostrophe. I'm sorry I flew off the handle. I hope it's
uncharacteristic.

> I admit my post was made in some haste; I am excited about a new project I
> hope to start soon therefore did not have the foresight to gather the Oxford
> English dictionary and Roget's thesaurus and ready myself properly for the
> almighty task of putting together a request on an internet newsgroup.
>
>
>
> So am I to gather from Mr Jerry Avins' comments that I am in fact not
> welcome here? Is this some sort of clique that only seasoned professional
> electronic engineers with an exquisite command of the English language can
> attend and pass comment and judgment upon the naive wanderer who may
> actually just only require some gentle advice? A prod or push in the right
> direction so to speak?

Not at all. Welcome is extended to all except perpetual boors. As an
occasional boor, I seem to be tolerated.

> If my question was not an acceptable one please someone point out why? I was
> under the impression if you were polite enough and I have no reason to
> suspect my post was not, some advice could be asked of the high and mighty
> knowledgeable of the internet brethren.

Had I known how to answer intelligently, I would have appended my
contribution to my tirade. My silence on the matter was the result of
ignorance, not pique.

> Anyway it's now approaching 3AM in London, so I must close this case. I
> apologise for any inconvenience caused as only a misplaced comma can.
>
>
>
> AL.

Good luck with your project.

Jerry
--
Engineering is the art of making what you want from things you can get.
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯

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?

--
Stephan M. Bernsee
http://www.dspdimension.com

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

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.
> ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
>

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?
(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.
> > ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯ ¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
> >
>
>

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

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

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

Steve Underwood wrote:

> 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.

—————————————————————————————————————————————————— —————————————————————

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.u k...
> 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!
>
>

On 2004-09-22 16:32:33 +0200, "Rob Vermeulen"
<rvermeulen@arbor-audio-antispam-.com> said:
>
> Ok, Al. Have you read the dspdimension pages?
> (http://www.dspdimension.nl). [...]

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