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<p>Xilinx says this about direct Digital Synthesis . "<span
style="color: rgb(0, 0, 0); font-family: "Open Sans",
sans-serif; font-size: 14px; font-style: normal;
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-webkit-text-stroke-width: 0px; background-color: rgb(255, 255,
255); text-decoration-style: initial; text-decoration-color:
initial; display: inline !important; float: none;">The core has
optional phase offset capability, providing support for multiple
synthesizers with precisely controlled phase differences." IS
this something that can be changed in realtime through software
or is it like a preset value. If it were changeable then it
seems like it could be used for waveshaping. <br>
</span></p>
<p><span style="color: rgb(0, 0, 0); font-family: "Open
Sans", sans-serif; font-size: 14px; font-style: normal;
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-webkit-text-stroke-width: 0px; background-color: rgb(255, 255,
255); text-decoration-style: initial; text-decoration-color:
initial; display: inline !important; float: none;">I'm trying to
get their ISE package running so I can mess with the technology
. I have a long , long way to go before I understand what the
heck is going on. <br>
</span></p>
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Sans", sans-serif; font-size: 14px; font-style: normal;
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255); text-decoration-style: initial; text-decoration-color:
initial; display: inline !important; float: none;"><br>
</span></p>
<p><span style="color: rgb(0, 0, 0); font-family: "Open
Sans", sans-serif; font-size: 14px; font-style: normal;
font-variant-ligatures: normal; font-variant-caps: normal;
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-webkit-text-stroke-width: 0px; background-color: rgb(255, 255,
255); text-decoration-style: initial; text-decoration-color:
initial; display: inline !important; float: none;">Mike<br>
</span></p>
<br>
<div class="moz-cite-prefix">On 4/20/2017 7:45 PM, Scott Gravenhorst
wrote:<br>
</div>
<blockquote cite="mid:20170420234528.7296C1A019E4@pi3c.lan"
type="cite">
<pre wrap="">
Interesting discussion.
My first FPGA subtractive synth was a 4 osc with naive waveforms. I did that because the
DAC was capable of 1 MHz sample rate which I used. Harmonics above 500 kHz are so low in
amplitude as to be negligible. I could portamento without siren fear. The drawback was
that it's 1 MHz DAC was also only 12 bits (the Spartan 3E Starter Kit board). However, the
12 bit-ness didn't really seem to degrade it's sound. But still, aliasing is aliasing and
a good high sample rate is one of the cures. It allows the simplicity of generating
waveforms in a naive manner.
Tom Wiltshire <a class="moz-txt-link-rfc2396E" href="mailto:tom@electricdruid.net"><tom@electricdruid.net></a> wrote:
</pre>
<blockquote type="cite">
<pre wrap="">Ok, so let's just have a look at that for a moment.
Assume a highest output frequency of 20KHz (I wouldn't even be
able to hear this). We've got a nyquist frequency of 12MHz. That
means that only anything that goes far enough over 12MHz to alias
all the way back down below 20KHz is actually going to be
audible. So that's 23.98MHz before we get audible aliasing.
That's equivalent to the 1199th harmonic of 20KHz ramp wave.
It's a high enough frequency they can ignore aliasing, even for
naive waveforms, and even for tough cases like ramps and squares.
It does seem like overkill, but FPGAs are cheap these days, and
running a few (or a lot of) NCOs isn't even going to make one
break a sweat.
Yeah, why not? I like it. Simple, direct, does the job.
Tom
On 20 Apr 2017, at 18:20, Richie Burnett <a class="moz-txt-link-rfc2396E" href="mailto:rburnett@richieburnett.co.uk"><rburnett@richieburnett.co.uk></a> wrote:
</pre>
<blockquote type="cite">
<pre wrap="">An interesting direction Novation are taking with the use of
</pre>
</blockquote>
<pre wrap="">FPGA based NCO oscillators on their new hybrid polysynth. There's
a video from Superbooth about it on sonicstate. It uses a sample
rate of 24MHz to generate classic analog saw, pulse, tri waves,
etc, then feeds them through conventional analog VCF, VCA, etc. >
</pre>
<blockquote type="cite">
<pre wrap="">Seems like a bit of a brute force way to crack the old aliasing
</pre>
</blockquote>
<pre wrap="">nut, but I guess it gives them the ability to do some wacky audio
rate modulation stuff with reduced aliasing too. > > -Richie, > >
Sent from my Xperia SP on O2 > >
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</pre>
</blockquote>
<pre wrap="">
-- ScottG
________________________________________________________________________
-- Scott Gravenhorst
-- <a class="moz-txt-link-freetext" href="http://scott.joviansynth.com/">http://scott.joviansynth.com/</a>
-- When the going gets tough, the tough use the command line.
-- Matt 21:22
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</pre>
</blockquote>
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