FPGA Central

Hello,

I have been seeing references to both synchronous and asynchronous
sample rate conversion. I just wanted to ask what the difference is
between the two. Is it that input and output clocks cannot be expected
to be in sync (apart from the out-of-sync properties that the rate
difference in itself poses)?

Morgan

Hi,

May I know about some of these references? I've been looking for that kind
of info.

Regards,

JaaC

Hi,

Synchronous Sample Rate Converter is used when both input and output
clocks are derived from the same source. For example speaker and
microphone having different sample rate but the clock is derived from
same crystal oscillator. In these type of Sample Rate Converter a
fixed rational ratio P/Q is good enough. In asynchronous Sample Rate
Converter the input and output clocks are derived from different
sources. Like copying one CD to another CD. Even though both are
having same speed, the clocks are derived from different sources and
hence a small variation will lead to big differences over a period of
time. For this normally one of the clock will be adjusted through PLL
or asynchronous Sample Rate Converter will be used.

Anandh
DSP Consultant
Kaliru Systems.


[email protected] (Morgan P?lsson) wrote in message news:<[email protected] com>...
> Hello,
>
> I have been seeing references to both synchronous and asynchronous
> sample rate conversion. I just wanted to ask what the difference is
> between the two. Is it that input and output clocks cannot be expected
> to be in sync (apart from the out-of-sync properties that the rate
> difference in itself poses)?
>
> Morgan

Just to add on a little bit, with asynchronous SRC, the ratio may change with
time, i.e. it is not constant. Often, you don't know explicitly what the ratio
is either and you have to measure it as you go (often with a software PLL).

"P. Anandh" <[email protected]> wrote in message
news:[email protected] om...
> Hi,
>
> Synchronous Sample Rate Converter is used when both input and output
> clocks are derived from the same source. For example speaker and
> microphone having different sample rate but the clock is derived from
> same crystal oscillator. In these type of Sample Rate Converter a
> fixed rational ratio P/Q is good enough. In asynchronous Sample Rate
> Converter the input and output clocks are derived from different
> sources. Like copying one CD to another CD. Even though both are
> having same speed, the clocks are derived from different sources and
> hence a small variation will lead to big differences over a period of
> time. For this normally one of the clock will be adjusted through PLL
> or asynchronous Sample Rate Converter will be used.
>
> Anandh
> DSP Consultant
> Kaliru Systems.
>
>
> [email protected] (Morgan P?lsson) wrote in message
news:<[email protected] com>...
> > Hello,
> >
> > I have been seeing references to both synchronous and asynchronous
> > sample rate conversion. I just wanted to ask what the difference is
> > between the two. Is it that input and output clocks cannot be expected
> > to be in sync (apart from the out-of-sync properties that the rate
> > difference in itself poses)?
> >
> > Morgan