Hello everybody,
I am writing a simple am modulator (actually ssb, but it does not really matters :) ). This
script shall take as input an audio signal and give as output the am modulated signal.

The problem I am facing is the following.
The input audio signal as, for instance, a sampling frequency of 8kHz. In the am modulator
script I have much higher frequency rates: the carrier has a frequency of 20 kHz and therefore
my highest frequency can become 28 kHz, which means 56 kHz of sampling frequency.
All this results in a really big mess one it comes to plot the results: indeed the input signal
has one sampling frequency but the script works at another (higher) sampling frequency.

How can I go around this problem?
Ive thought about upsampling, but this creates longer vectors which mess up my script!! :S

thank you for your help! :)

mathias

Keep your sampling frequency according to the highest frequency
expected in your system

maybe a simple matlab example helps...

clear all
T = 1/100;
fm = 0.25
fc = 10
mt = sin(2*pi*fm*[0:T:10])
ct = sin(2*pi*fc*[0:T:10]);
yt = mt.*ct;
plot(yt)

Krishna
http://www.dsplog.com

On 10/20/07, m...@gmail.com <m...@gmail.com> wrote:
> Hello everybody,
> I am writing a simple am modulator (actually ssb, but it does not really
> matters :) ). This script shall take as input an audio signal and give as
> output the am modulated signal.
>
> The problem I am facing is the following.
> The input audio signal as, for instance, a sampling frequency of 8kHz. In
> the am modulator script I have much higher frequency rates: the carrier has
> a frequency of 20 kHz and therefore my highest frequency can become 28 kHz,
> which means 56 kHz of sampling frequency.
> All this results in a really big mess one it comes to plot the results:
> indeed the input signal has one sampling frequency but the script works at
> another (higher) sampling frequency.
>
> How can I go around this problem?
> Ive thought about upsampling, but this creates longer vectors which mess up
> my script!! :S
>
> thank you for your help! :)
>
> mathias
>