# How to reproduce a sound sample algorithmically?

A

#### [email protected]

Jan 1, 1970
0
I need to reproduce a certain sound wave form, specifically, the sound
of a heartbeat, and I need to do it with only a few dozen bytes of ram,
on a PIC MCU. The sample itself is 250ms long, and I have it in
uncompressed audio format at 11khz, 8 bits, mono. Is there a way to
create a mathematical algorithm to generate the sound on the PIC?
Otherwise I would need 344 bytes of ram, and thats more than the PIC
has total not including the ram needed for code and all the other stuff
I am doing on it. The heartbeat must be exacly reproduced, so I cant
just generate an approximation.

O

#### [email protected]

Jan 1, 1970
0
I need to reproduce a certain sound wave form, specifically, the sound
of a heartbeat, and I need to do it with only a few dozen bytes of ram,
on a PIC MCU. The sample itself is 250ms long, and I have it in
uncompressed audio format at 11khz, 8 bits, mono. Is there a way to
create a mathematical algorithm to generate the sound on the PIC?
Otherwise I would need 344 bytes of ram, and thats more than the PIC
has total not including the ram needed for code and all the other stuff
I am doing on it. The heartbeat must be exacly reproduced, so I cant
just generate an approximation.

Use a piecewise function? Try using gnuplot to get a curve fitted for
the pieces. But, geez, only 344 bytes of RAM? Can't you get any more?

D

#### Damir

Jan 1, 1970
0
I need to reproduce a certain sound wave form, specifically, the sound
of a heartbeat, and I need to do it with only a few dozen bytes of ram,
on a PIC MCU. The sample itself is 250ms long, and I have it in
uncompressed audio format at 11khz, 8 bits, mono. Is there a way to
create a mathematical algorithm to generate the sound on the PIC?
Otherwise I would need 344 bytes of ram, and thats more than the PIC
has total not including the ram needed for code and all the other stuff
I am doing on it. The heartbeat must be exacly reproduced, so I cant
just generate an approximation.

Maybe this could help: http://www.romanblack.com/picsound.htm

J

#### [email protected]

Jan 1, 1970
0
You say you say that the heartbeat must be exactly reproduced, but in
practical digital sampling and sound reproduction there are only better
or worse approximations to the original. How bad can you accept?

If you just want to play back the one sound then there's no need to
store it in RAM. Put it in program ROM using a jump table and the RETLW
instruction. But where does the figure 344 bytes of RAM come from? Are
you already compressing it? It seems to me that if you stick to 250ms
at 11Khz you will need 2750 bytes.

S

#### Spehro Pefhany

Jan 1, 1970
0
I need to reproduce a certain sound wave form, specifically, the sound
of a heartbeat, and I need to do it with only a few dozen bytes of ram,
on a PIC MCU. The sample itself is 250ms long, and I have it in
uncompressed audio format at 11khz, 8 bits, mono. Is there a way to
create a mathematical algorithm to generate the sound on the PIC?
Otherwise I would need 344 bytes of ram, and thats more than the PIC
has total not including the ram needed for code and all the other stuff
I am doing on it. The heartbeat must be exacly reproduced, so I cant
just generate an approximation.

If you just store it in ROM, it will require 2750 words of memory
(assuming 12 or 14-bit instructions, half that with 16-bit
instructions), and almost no RAM. ADPCM is a compression scheme that
requires little processing and might be suitable for you. Any lossy
compression scheme is not going to be an "exact" reproduction.

Do a Fourier analysis and see where the energy is. I just tried that
with a sfx 'heartbeat', and most of it was below 1500Hz, so maybe you
could go lower on the sample rate. If you could use 5500Hz and use 1/2
word per sample, it would only be 690 words of ROM.

Now, algorithmically- the sfx heartbeat looks like about half a dozen
cycles at around 100Hz, decreasing in frequency, followed and preceded
by some ~80Hz with a little 800Hz on top, fairly constant amplitude
before and lower/decreasing with time amplitude (envelope) after. This
sfx sound would not be that hard to program, and would use less ROM.

Best regards,
Spehro Pefhany

J

#### John B

Jan 1, 1970
0
If you just store it in ROM, it will require 2750 words of memory
(assuming 12 or 14-bit instructions, half that with 16-bit
instructions), and almost no RAM. ADPCM is a compression scheme that
requires little processing and might be suitable for you. Any lossy
compression scheme is not going to be an "exact" reproduction.

Do a Fourier analysis and see where the energy is. I just tried that
with a sfx 'heartbeat', and most of it was below 1500Hz, so maybe you
could go lower on the sample rate. If you could use 5500Hz and use 1/2
word per sample, it would only be 690 words of ROM.

Now, algorithmically- the sfx heartbeat looks like about half a dozen
cycles at around 100Hz, decreasing in frequency, followed and preceded
by some ~80Hz with a little 800Hz on top, fairly constant amplitude
before and lower/decreasing with time amplitude (envelope) after. This
sfx sound would not be that hard to program, and would use less ROM.

Best regards,
Spehro Pefhany

It would be much easier to store the data in an external 8-bit EPROM and just use the PIC to

J

#### Jonathan Kirwan

Jan 1, 1970
0
I need to reproduce a certain sound wave form, specifically, the sound
of a heartbeat, and I need to do it with only a few dozen bytes of ram,
on a PIC MCU. The sample itself is 250ms long, and I have it in
uncompressed audio format at 11khz, 8 bits, mono. Is there a way to
create a mathematical algorithm to generate the sound on the PIC?
Otherwise I would need 344 bytes of ram, and thats more than the PIC
has total not including the ram needed for code and all the other stuff
I am doing on it. The heartbeat must be exacly reproduced, so I cant
just generate an approximation.

Spehro Pefhany's comment about looking at the FFT is good, though I'm
not sure that will get you anywhere close to the "few dozen bytes of
RAM" region. I'm not sure why you can't use flash or ROM to store the
image, but let's say you can't do that for some reason and want the
absolute smallest possible footprint.

I don't have direct experience with this, but you might take a look at
the possibility of using linear predictive coding and Huffman
compression. Take a look at "Numerical Recipes" for some discussion.

Some creativity may be needed, as well. One thing that comes to mind
also is continued fractions, but a discussion of the idea would take a
while and I'm not even sure exactly how to consider applying them
without thinking a lot more about it. Or if, in fact, the idea even
can be well applied.

Jon

T

#### Tim Shoppa

Jan 1, 1970
0
The heartbeat must be exacly reproduced, so I cant
just generate an approximation.

Well, I can tell you that envelope-modulating some pink noise will be a
pretty damn good approximation.

But now you're telling us that only the exact thing is needed.

If someone else is telling you that "exactly" is the only way, then you
just have to tell them how much to budget for it.

Sounds like a lot of my former and too many of my current customers
.

Tim.

S

#### Spehro Pefhany

Jan 1, 1970
0
It would be much easier to store the data in an external 8-bit EPROM and just use the PIC to

Or a 50-cent 8-pin 32-K SPI SEEPROM, but where's the fun in that, eh?

Best regards,
Spehro Pefhany

J

#### John Perry

Jan 1, 1970
0
I need to reproduce a certain sound wave form, specifically, the sound
of a heartbeat, and I need to do it with only a few dozen bytes of ram,
on a PIC MCU. The sample itself is 250ms long, and I have it in
uncompressed audio format at 11khz, 8 bits, mono. Is there a way to
create a mathematical algorithm to generate the sound on the PIC?
Otherwise I would need 344 bytes of ram, and thats more than the PIC
has total not including the ram needed for code and all the other stuff
I am doing on it. The heartbeat must be exacly reproduced, so I cant
just generate an approximation.

First, to get the principles out of the way, you have an approximation
with your recording. It may be a good approximation, but it's still
only an approximation. Your decision is going to be how good must your
new approximation be, and what are the real criteria for deciding what

Second, where do you get the 344 bytes number? 11KHz * .25 second =
2750 samples, which sounds very much like 2750 bytes. And, since the
typical heartbeat period is around 850ms, what do you really have? Only
the most obvious pulse, with none of the little stuff that goes on
between big pulses, or not even all of the main pulse?

Now, you have to decide what kind of accuracy you need in your
approximation. You already have a rather coarse 8 bits in your sample,
so experimenting with various piecewise leastsquares curve fits may give
an approximation as good as what you have, and save you some RAM at the
expense of some processing time. Or, a simple linear interpolation
between pairs of points at times selected to minimize slope errors --
assuming that's even important.

Next, if you have it pre-recorded, why not use a much better processor
than the PIC? For what you want to do I don't know of any processor
worse designed than the PIC (at least the 16... series, which are all
I've used). Use a decent processor and you can copy your entire sample
set out from flash at 11KHz.

John Perry

PS -- The PIC16 is atrocious for this kind of job, but it works OK for
other kinds of applications. Don't read more into my comment than I say.

G

#### Genome

Jan 1, 1970
0
I need to reproduce a certain sound wave form, specifically, the sound
of a heartbeat, and I need to do it with only a few dozen bytes of ram,
on a PIC MCU. The sample itself is 250ms long, and I have it in
uncompressed audio format at 11khz, 8 bits, mono. Is there a way to
create a mathematical algorithm to generate the sound on the PIC?
Otherwise I would need 344 bytes of ram, and thats more than the PIC
has total not including the ram needed for code and all the other stuff
I am doing on it. The heartbeat must be exacly reproduced, so I cant
just generate an approximation.

You am TWAT.

WE AM TRYING TO DISCUSS POLIT/RELIG/GLOBSTUFF IN THIS FORUM HERE AND YOU AM
GAY IN FROM CALIF AND GO BLAH.

YOU FINK YOU AM CLEV OR WOT?

I am report you for absing yur dog to FIB.

There...

DNA

B

#### bruce varley

Jan 1, 1970
0
I need to reproduce a certain sound wave form, specifically, the sound
of a heartbeat, and I need to do it with only a few dozen bytes of ram,
on a PIC MCU. The sample itself is 250ms long, and I have it in
uncompressed audio format at 11khz, 8 bits, mono. Is there a way to
create a mathematical algorithm to generate the sound on the PIC?
Otherwise I would need 344 bytes of ram, and thats more than the PIC
has total not including the ram needed for code and all the other stuff
I am doing on it. The heartbeat must be exacly reproduced, so I cant
just generate an approximation.

A thought based on minimal information....Try outputting a square pulse then
analog filtering it with a multipole filter to make a click into a thump. If
you can get a single thump sounding just about right, then it might be just
a matter of the micro outputting the right length digital pulses, which
should be esy to do with your memory allowance.

B

#### [email protected]

Jan 1, 1970
0
I need to reproduce a certain sound wave form, specifically, the sound
of a heartbeat, and I need to do it with only a few dozen bytes of ram,
on a PIC MCU. The sample itself is 250ms long, and I have it in
uncompressed audio format at 11khz, 8 bits, mono. Is there a way to
create a mathematical algorithm to generate the sound on the PIC?
Otherwise I would need 344 bytes of ram, and thats more than the PIC
has total not including the ram needed for code and all the other stuff
I am doing on it. The heartbeat must be exacly reproduced, so I cant
just generate an approximation.

If you have got access to a least square curve fitting package it may
be able to find you a moderately simple mathermatical function that you
can fit to the waveform by adjusting two or three parameters - many
real impulse signals can be fitted as an exponential decay (where the
exponent is complex, in the sense of including imaginary numbers).

Whether you can then generate the function in the remaining bytes of
RAM is an open question.

K

#### Ken Smith

Jan 1, 1970
0
John B said:
It would be much easier to store the data in an external 8-bit EPROM and
just use the PIC to

Or better yet, use one of the many 8051 like chips that has 64K or so of
code space. The 8051s can nest subroutines more than 40 deep. This would
allow a lot of reuse of segments of the curve with fairly simple coding.

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