[sdiy] ATSamD4 Breakout Board

Mikko Helin maohelin at gmail.com
Tue Nov 10 10:23:14 CET 2015


Regarding STM32 and related IDE's Atollic has just removed the code size
limitation from Truestudio Lite, so it is now easier to use it with CubeMX
tool than mess with the Eclipse CDT & plugins route:

http://timor.atollic.com/truestudio/

-Mikko

On Tue, Nov 10, 2015 at 8:51 AM, <rsdio at audiobanshee.com> wrote:

>
> On Nov 9, 2015, at 2:06 PM, nvawter <nvawter at media.mit.edu> wrote:
> > On 2015-11-09 16:32, Eric Brombaugh wrote:
> >> It works fine but the 12-bit output might be limiting in some
> situations.
> >
> > IIRC this app note correctly:
> http://www.atmel.com/Images/doc8003.pdf
> >
> > It shows how N bit sampling can be turned into N+M bit samples through
> oversampling at (4^M) times.  I think this would work well for DACs, too.
> >
> > That (4^M) sounds very expensive to do, but there is a sweet spot in
> turning 12-bit into 14-bit by upsampling 16x.  14-bit = 12-bit * (2^2).
> That would mean a 44 kHz output routine would have to run a 705 kHz routine
> to upsample and synthesize a new sample every 16 times (@44kHz), but I
> believe the oversampling math is nearly the same as linear interpolation.
> (you don't have to re-synth the whole synth loop at 705 kHz, only do the
> interp).
> >
> > Something to think about!  I'd love to try it sometime...   could be an
> easy experiment even with something like my Teensy 3.1....
> This is a great technique when you need to scan faders and knobs at 100
> Hz, and have the headroom to bump that up to 1.6 kHz. However, I strongly
> recommend against trying to run samples through a tiny processor at 705.6
> kHz. It's just not very efficient to handle things at that high of a rate
> with a general-purpose CPU. Far better to just bite the bullet and get an
> I2S CODEC that can handle 16-bit at 44.1 kHz. You'll probably find that the
> 12-bit ADC can't handle those rates anyway. By the time you find a 12-bit
> CODEC that can handle those rates - I've designed with Texas Instruments
> chips that handle 1 MHz sampling - you're already external to the CPU and
> should probably just switch to a 16-bit native chip. There are drawbacks to
> oversampling.
>
>
> > Also on the topic STM and oversampling: I took a seminar on the STM32L4
> (low-power STM32F4) last month...  The newer parts have *built-in*
> oversampling on the ADC side!  I think it went up to 256x?  I haven't
> researched what other parts have this as well, but I wouldn't be surprise
> to see it propagate into others.  It also has a built-in convolution for up
> to 1024x sigma-delta samples!  amazing age we live in…
> In this case, hardware oversampling is much more efficient, and simply
> delivers the down-sampled to your CPU. Most audio CODEC chips these days
> operate in delta-sigma mode with serious oversampling to increase the bit
> depth. In fact, all 24-bit chips operate with oversampling.
>
> Brian
>
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