Setting sample rates for human audible recorded voice.

[nikhilrajg]

Hello All,

How to set sample rates in PIC24F microcontroller. ?

I am using PIC24F128GA010 micro and want to sample the recorded voice so that the human can listen to it clearly. I can record the voice and I can even play it. After once I play it I just here some noise just as if we tune to some unknown radio-play station !!!!! :sad: I here only noice and nothing else. And this is the rate at which am sampling it.. How to do this and what values will be best suitable for this ?

Can I use Timer interrupt for this ?

Please help..

Thanks.
Nikhil Raj.

 

[jokkebk]

Don't know about the specifics of PIC23F configuration, but usual sampling rates for voice are 22 kHz or sometimes even just 11 kHz (saves a bit space but I guess high frequency components do get cut off).

I would also consider the possibility that for some reason the microphone is not transmitting the signal adequately to the MCU - check if it for example requires pre-amplification before being fed to the PIC, otherwise you may just record nothing (although hearing a lot of noise seems to contradict that, unless you over-amplify the output).

 

[nikhilrajg]

Don't know about the specifics of PIC23F configuration, but usual sampling rates for voice are 22 kHz or sometimes even just 11 kHz (saves a bit space but I guess high frequency components do get cut off).

I would also consider the possibility that for some reason the microphone is not transmitting the signal adequately to the MCU - check if it for example requires pre-amplification before being fed to the PIC, otherwise you may just record nothing (although hearing a lot of noise seems to contradict that, unless you over-amplify the output).

My PIC i.e., PIC24FJ128GA010 I can give analog input volts only within 2 to 3.6 volts. So as you said 1st I used an amplifier LM324 to amplify the voice. But It was exceeding the PIC's limits. So I removed the amplifier and mocified the circuit and for now the values are suitable for the PIC. My doubt is how to use Timer-3 as an interrupt handler to sample the voice ?

Say for example... How to set 44uS for 22050 samples/second ?? I mean the value to be set for the sampling rate ???

Thank You
Nikhil Raj.

- - - Updated - - -

Then can you please tell how to set that frequency ?? As you said its 22khz

Regards.
Nikhil Raj

 

[paulfjujo]

hello


Before, You have to check what is the mimimum time to get a valide sample from the ADC part.
i don't know PIC24F , but theses information must be in datasheet.
This will give you an idee about the maximum sample rate .
Don't forget to add the duration of treatment ( store data ,time to go into interrupt .. etc..)

 

[nikhilrajg]

Hello paul !

Thank You for reply.

Are you talking about the internal oscillator frequency ?
If yes from the datasheet..

All of the devices in the PIC24FJ128GA010 family offer
five different oscillator options, allowing users a range
of choices in developing application hardware. These
include:
• Two Crystal modes using crystals or ceramic
resonators.
• Two External Clock modes offering the option of a
divide-by-2 clock output.
• A Fast Internal Oscillator (FRC) with a nominal
8 MHz output, which can also be divided under
software control to provide clock speeds as low as
31 kHz.
• A Phase Lock Loop (PLL) frequency multiplier,
available to the external oscillator modes and the
FRC oscillator, which allows clock speeds of up to
32 MHz.
• A separate internal RC oscillator (LPRC) with a
fixed 31 kHz output, which provides a low-power
option for timing-insensitive applications.
The internal oscillator block also provides a stable reference
source for the Fail-Safe Clock Monitor. This
option constantly monitors the main clock source
against a reference signal provided by the internal
oscillator and enables the controller to switch to the
internal oscillator, allowing for continued low-speed
operation or a safe application shutdown.

Thanks
Nikhil