[CART360] CART 360 _Arduino 'sample rate'

[Morgan Sutherland]

The R2-R ladder used 1 output from the Arduino. How does adding a bunch of
resistors add sample resolution to a signal that was originally 1-bit?
That's a rhetorical question – it can't – but perhaps it interpolates?
Ah, the wikipedia article[1] leads me to believe that this is the case (as
it describes the circuit as useful for D/A conversion).

1. http://en.wikipedia.org/wiki/Resistor_ladder

On Sat, Oct 17, 2009 at 10:37 AM, Vincent Leclerc <v at uttermatter.com> wrote:

> Hi Jon,
>
> This is often confusing. There is a big difference in sample rate and
> sample resolution. I added a graphic at the bottom of:
> http://hybrid.concordia.ca/~cart360_vincent/studio/05/
>
> The 2 graphs show 2 completely different sound samples.
>
> The first graph shows a 1-bit resolution sound sample and the second
> shows an 8-bit resolution sound sample. That is sample resolution.
>
> Now for sample rate -- the amount of samples you record (or generate)
> per second -- you can see that at [a, b, c] we record samples at the
> same time. In the 1-bit resolution sample, you always record 5V, but
> for the 8-bit sample we record [2.5V, 1.88V, 1.25V]. This is why
> sample resolution is as important as sample rate.
>
> Generally the Arduino outputs with a single digital pin, so it outputs
> at a 1-bit resolution, regardless of your sample rate (which can be
> quite surprisingly high as you said in class).
>
> If you want 8-bit resolution output, R-2R ladders are the
> easiest/cheapest way to go about it.
>
> http://blog.makezine.com/archive/2008/05/makeit_protodac_shield_fo.html?CMP=OTC-0D6B48984890
>
> Hope it makes things clearer.
>
> Vincent
>
>
> On Fri, Oct 16, 2009 at 10:33 PM, joN <jonnygexter at gmail.com> wrote:
> > Hi.
> >
> > There's something confused in my understanding of sampling (or the
> opposite,
> > reconstructing)..
> >
> > I was thinking about what you said in class when I mentioned the Arduino
> was
> > shooting out samples at a rate equivalent to a CD player. Did you say
> that
> > the resolution of the Arduino is be one BYTE or one BIT?
> >
> > Using digital out means the speaker is either HIGH or LOW, which would be
> > equivalent of one BIT. But my guess is that the voltage being either high
> or
> > low relates to amplitude.
> >
> > On the other hand, if you said one BYTE, I would think you meant the
> integer
> > stored as the timeHigh value (time period to switch the speaker
> HIGH/LOW),
> > (though the Arduino reference says that ints are stored as 2 bytes). If
> this
> > is what you were referring to, then my thinking is that this value
> relates
> > to the possible quantized units, as in discrete, non-analog values, I can
> > use to set the frequency.
>
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