On 20/09/15 03:43, Tomas Härdin wrote:
> Couldn't you do further low-pass filtering in software, then decimate to
> 8 kHz? (caveat: I haven't checked if the code actually does this)
That's exactly what it does. It samples at 16kHz from the ADC, filters
it to produce an 8kHz stream.
Actually a
I don't think a linear interpolator would work here. There's quite a bit of
attenuation in the 0-Fs/4 band (~8dB by Fs/8) and only around -28dB on the
aliases. -28dB might be enough for the aliases, but I don't think it's flat
enough in the Fs/4 band to be useful.
Couldn't you do further low-pass filtering in software, then decimate to
8 kHz? (caveat: I haven't checked if the code actually does this)
/Tomas
On Fri, 2015-09-18 at 16:13 +1000, glen english wrote:
> Hi Stuart
>
> An elaboration on David's reply.
>
> We want our audio BW to go to at least
Hi Stuart
An elaboration on David's reply.
We want our audio BW to go to at least say 3.4 kHz . That is what
fixed line telephones offer.
If we were to sample at 8kHz, our nyquist frequency is 4kHz of
course.
Any spectral information above the
Hi David & Glen,
On 18/09/15 16:13, glen english wrote:
> If we were to sample at 8kHz, our nyquist frequency is 4kHz of course.
> Any spectral information above the nyquist rate will be aliased bay into
> the baseband, IE below the nyquist rate.
>
> IF we assume we don't care about aliases
Also there is very little speech energy out past 12 kHz, i.e. its
already 50dB down, and this is communications quality speech so a little
aliasing is lost in the codec artefacts.
On the radios interface side the audio is band limited by the radio's
frequency response, ie the xtal filter BW.
yeah you can pretty much get away with NO aliasing filter considering
the source ( a band limited microphone) and the required voiceband SN.
still, good reason to have at least a single RC- from say switchmode
power supply whistles etc getting back into the input, and aliasing down
into the
Hi Stuart,
Running the ADC/DAC at 16 kHz largely removes the need for analog
anti-aliasing/reconstruction filters, significantly simplifying the
hardware.
- David
On 17/09/15 19:23, Stuart Longland wrote:
> Hi all,
>
> Just looking at the source code, it hit me. When in analogue mode, we
>
