>> If you want to vary the speed of more general signals, like music, try
>> http://www.dspdimension.com/category/tutorial/
>>
>> Steve
>
>
> Jerry also recommended the above mention site. It seems like the buzz word
> is "Time streching" rather than slow motion. At least I now know the
> correct terminology in what I am trying to accomplish. Thanks.
>
> The phase vocoder seems to be a candidate for my design.
>
> "dspdimension" gives some code for pitch shifting. It is not what I
> originally asked for. Nevertheless, I am currently working with it. On the
> other hand, writing Time Streching code is going to be more challenging.
It's the same code, with a trivial step removed. To stretch the time,
you reduce the playback rate (which shifts the pitch down) then shift
the pitch up to compensate.
Jerry
--
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������
Jerry also recommended the above mention site. It seems like the buzz word
is "Time streching" rather than slow motion. At least I now know the
correct terminology in what I am trying to accomplish. Thanks.
The phase vocoder seems to be a candidate for my design.
"dspdimension" gives some code for pitch shifting. It is not what I
originally asked for. Nevertheless, I am currently working with it. On the
other hand, writing Time Streching code is going to be more challenging.
Reply by Steve Underwood●January 9, 20082008-01-09
Stacy wrote:
> How do you slow down a digital audio recording and keep the same pitch?
>
> For example if the audio sample was recorded at 44.1k you could, by S/W
> intervention, tell it to play at 22.05k. That will slow it down by half
> speed. However, it will also lower the pitch by half also.
>
> The approach I would take to slow down by 2 is:
> 1) Find a way to double the frequency of the audio sample. I would try to
> accomplish this by
> i) taking the FFT,
> ii) moving the values in the bins to what is double the frequency,
> iii) then taking the iFFT.
>
> 2) Tell the recorder to play at 22.05k.
>
> What say you?
I say it depends on the signal. What works pretty well for speech may
suck for music. What you are suggesting sound pretty nasty for speech.
If you want to vary the playback speed of speech try Googling for TDHS,
PSOLA, PICOLA, and a few related ideas should pop up along the way.
If you want to vary the speed of more general signals, like music, try
http://www.dspdimension.com/category/tutorial/
Steve
Reply by Ron N.●January 9, 20082008-01-09
On Jan 8, 6:30 pm, "Stacy" <stacy2003_yo...@yahoo.com> wrote:
> How do you slow down a digital audio recording and keep the same pitch?
>
> For example if the audio sample was recorded at 44.1k you could, by S/W
> intervention, tell it to play at 22.05k. That will slow it down by half
> speed. However, it will also lower the pitch by half also.
>
> The approach I would take to slow down by 2 is:
> 1) Find a way to double the frequency of the audio sample. I would try to
> accomplish this by
> i) taking the FFT,
> ii) moving the values in the bins to what is double the frequency,
> iii) then taking the iFFT.
>
> 2) Tell the recorder to play at 22.05k.
>
> What say you?
For this 2X case: What do you do with the contents of
bins at or above one fourth the sample rate? And what
do you put in the odd numbered bins?
You might want to look up: low pass filtering by one
of the FFT overlap methods and phase vocoder methods
for time/pitch modification.
IMHO. YMMV.
--
rhn A.T nicholson d.0.t C-o-M
Reply by Richard Dobson●January 9, 20082008-01-09
Fred Marshall wrote:
..
>>Google for Phase Emcoder.
>
>
> Never heard of it but I tried:
>
> ["Phase Emcoder"] yields nothing at all.
>
Should be "phase vocoder" - both time-scaling and pitch-shifting are
canonical tasks for it.
Richard Dobson
Reply by Fred Marshall●January 9, 20082008-01-09
"HardySpicer" <gyansorova@gmail.com> wrote in message
news:09ef8e29-a8ed-4e90-8cab-53f1c4f6fc84@s8g2000prg.googlegroups.com...
> On Jan 9, 6:53 pm, "Fred Marshall" <fmarshallx@remove_the_x.acm.org>
> wrote:
>> "Stacy" <stacy2003_yo...@yahoo.com> wrote in message
>>
>> news:BuSdnbF_xLFZrBnanZ2dnUVZ_saknZ2d@giganews.com...
>>
>>
>>
>> > How do you slow down a digital audio recording and keep the same pitch?
>>
>> > For example if the audio sample was recorded at 44.1k you could, by S/W
>> > intervention, tell it to play at 22.05k. That will slow it down by half
>> > speed. However, it will also lower the pitch by half also.
>>
>> > The approach I would take to slow down by 2 is:
>> > 1) Find a way to double the frequency of the audio sample. I would try
>> > to
>> > accomplish this by
>> > i) taking the FFT,
>> > ii) moving the values in the bins to what is double the frequency,
>> > iii) then taking the iFFT.
>>
>> > 2) Tell the recorder to play at 22.05k.
>>
>> > What say you?
>>
>> One interpretation of your question would be: "how to play it back at
>> half
>> the sample rate?"
>>
>> So why not decimate the samples first?
>>
>> Now, if what you want is to actually play it back slowly - i.e. words
>> come
>> out twice as long in time - then that's another matter. Useful though...
>>
>> Fred
>
> Google for Phase Emcoder.
Never heard of it but I tried:
["Phase Emcoder"] yields nothing at all.
[phase emcoder] yields a bunch of stuff that looks not pertinent and I
suspect a lot of typos meaning "encoder"
I think the most general method that applies is "speech encoding" or "linear
predictive speech encoding". Here is one quote:
"Bandwidth reduction is achieved by selecting perceptually significant
spectral regions and dropping the rest, through a proprietary technique"
Most hits are for patents...
Better, look for lectures on [LP speech lecture] and [CELP speech lecture]
and maybe add .ppt to the search to eliminate course outlines.
Fred
Reply by mnentwig●January 9, 20082008-01-09
AFAIK there is no ideal solution to this problem.
Reply by HardySpicer●January 9, 20082008-01-09
On Jan 9, 6:53 pm, "Fred Marshall" <fmarshallx@remove_the_x.acm.org>
wrote:
> "Stacy" <stacy2003_yo...@yahoo.com> wrote in message
>
> news:BuSdnbF_xLFZrBnanZ2dnUVZ_saknZ2d@giganews.com...
>
>
>
> > How do you slow down a digital audio recording and keep the same pitch?
>
> > For example if the audio sample was recorded at 44.1k you could, by S/W
> > intervention, tell it to play at 22.05k. That will slow it down by half
> > speed. However, it will also lower the pitch by half also.
>
> > The approach I would take to slow down by 2 is:
> > 1) Find a way to double the frequency of the audio sample. I would try to
> > accomplish this by
> > i) taking the FFT,
> > ii) moving the values in the bins to what is double the frequency,
> > iii) then taking the iFFT.
>
> > 2) Tell the recorder to play at 22.05k.
>
> > What say you?
>
> One interpretation of your question would be: "how to play it back at half
> the sample rate?"
>
> So why not decimate the samples first?
>
> Now, if what you want is to actually play it back slowly - i.e. words come
> out twice as long in time - then that's another matter. Useful though...
>
> Fred
Google for Phase Emcoder.
Hardy
Reply by Fred Marshall●January 9, 20082008-01-09
"Stacy" <stacy2003_young@yahoo.com> wrote in message
news:BuSdnbF_xLFZrBnanZ2dnUVZ_saknZ2d@giganews.com...
> How do you slow down a digital audio recording and keep the same pitch?
>
> For example if the audio sample was recorded at 44.1k you could, by S/W
> intervention, tell it to play at 22.05k. That will slow it down by half
> speed. However, it will also lower the pitch by half also.
>
> The approach I would take to slow down by 2 is:
> 1) Find a way to double the frequency of the audio sample. I would try to
> accomplish this by
> i) taking the FFT,
> ii) moving the values in the bins to what is double the frequency,
> iii) then taking the iFFT.
>
> 2) Tell the recorder to play at 22.05k.
>
> What say you?
One interpretation of your question would be: "how to play it back at half
the sample rate?"
So why not decimate the samples first?
Now, if what you want is to actually play it back slowly - i.e. words come
out twice as long in time - then that's another matter. Useful though...
Fred
Reply by Jerry Avins●January 8, 20082008-01-08
Stacy wrote:
> How do you slow down a digital audio recording and keep the same pitch?
>
> For example if the audio sample was recorded at 44.1k you could, by S/W
> intervention, tell it to play at 22.05k. That will slow it down by half
> speed. However, it will also lower the pitch by half also.
>
> The approach I would take to slow down by 2 is:
> 1) Find a way to double the frequency of the audio sample. I would try to
> accomplish this by
> i) taking the FFT,
> ii) moving the values in the bins to what is double the frequency,
> iii) then taking the iFFT.
>
> 2) Tell the recorder to play at 22.05k.
>
> What say you?
There's a whole body of practice in this area, some of it trade secrets.
I suggest you start at http://www.dspdimension.com/ and look on the
DOWNLOAD page.
Jerry
--
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������