MOTM

Hello all -

I just had an interesting session with my audio redcording software 
(in this case Cool Edit 2000).  I hooked a 300 directly to my console 
and recorded a bit of each waveform.  Did the same for the 310.

This is probably a great opportunity to show how knowledgeable I 
truly am.

Let's start with the SQUARE out: it's not square! It goes straight 
up, then exponentially down, creating a sort-of fast-attack 
exponential-decay wave form above zero, then inverts the same 
waveform below zero.  Could this be why the square output has always 
seemd a little buzzy to me?  Not a bad thing, mind you.

The SAW looks just like the positive half of the SQUARE, except that 
it dips below zero a couple of db.

The 310 OUT is the same as 300 SQUARE when 310 SHAPE is a 10.  SHAPE 
at 0 gives same as 300 SAW and shape at 5 is a combo of the two.

SO the stupid question: why isn't the SQUARE square and the SAW saw?

Mike

Your console is probably AC coupled so it's acting like a filter and 
changing the shape of the waveforms as well as removing any perceived 
DC bias. I test all my modules with a DC coupled scope and they look 
exactly as advertised.

>Let's start with the SQUARE out: it's not square! It goes straight
>up, then exponentially down, creating a sort-of fast-attack
>exponential-decay wave form above zero, then inverts the same
>waveform below zero.  Could this be why the square output has always
>seemd a little buzzy to me?  Not a bad thing, mind you.

Your sound card's sampling rate is way too low. Try bumping it up to 1 MHz
or so and the waveform will look very square.  ;-)

Seriously, that's what a square wave looks like without all the high
frequency harmonics. Kinda scary but normal.
-- 

Terry Bowman, KA4HJH
"The Mac Doctor"

"By the end of Chuck Statler's 'Rock Videos' of Devo we agreed that even if
Devo did not take the stage it was still the best concert any of us had
ever attended." --Kim Thayil (Soundgardern), 1995

mike, you say it sounds buzzy. there may be a pcb error (happened to me). 
just to be sure, check it with a scope on the DC setting.

mark


At 10:24 PM 3/20/02 +0000, you wrote:

>Hello all -
>
>I just had an interesting session with my audio redcording software
>(in this case Cool Edit 2000).  I hooked a 300 directly to my console
>and recorded a bit of each waveform.  Did the same for the 310.
>
>This is probably a great opportunity to show how knowledgeable I
>truly am.
>
>Let's start with the SQUARE out: it's not square! It goes straight
>up, then exponentially down, creating a sort-of fast-attack
>exponential-decay wave form above zero, then inverts the same
>waveform below zero.  Could this be why the square output has always
>seemd a little buzzy to me?  Not a bad thing, mind you.
>
>The SAW looks just like the positive half of the SQUARE, except that
>it dips below zero a couple of db.
>
>The 310 OUT is the same as 300 SQUARE when 310 SHAPE is a 10.  SHAPE
>at 0 gives same as 300 SAW and shape at 5 is a combo of the two.
>
>SO the stupid question: why isn't the SQUARE square and the SAW saw?
>
>Mike
>
>
>
>
>
>
>Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/

Thanks, Terry.  Glad to know I'm normal :) I've hadseveral replies to 
this post both on and off list.  I will summarize these tonight and 
post them.  I might also post screenshots of the waveforms.  I'm 
still alittle confused...

Mike

--- In motm@y..., KA4HJH <ka4hjh@g...> wrote:
> >Let's start with the SQUARE out: it's not square! It goes straight
> >up, then exponentially down, creating a sort-of fast-attack
> >exponential-decay wave form above zero, then inverts the same
> >waveform below zero.  Could this be why the square output has 
always
> >seemd a little buzzy to me?  Not a bad thing, mind you.
> 
> Your sound card's sampling rate is way too low. Try bumping it up 
to 1 MHz
> or so and the waveform will look very square.  ;-)
> 
> Seriously, that's what a square wave looks like without all the high
> frequency harmonics. Kinda scary but normal.
> -- 
> 
> Terry Bowman, KA4HJH
> "The Mac Doctor"
> 
> "By the end of Chuck Statler's 'Rock Videos' of Devo we agreed that 
even if
> Devo did not take the stage it was still the best concert any of us 
had
> ever attended." --Kim Thayil (Soundgardern), 1995

You are observing a "hidden" HPF (high pass filter), caused by the reactance of the AC coupling
network on the sound card.

Try increasing the VCO frequency to like '7' tick mark.

In order not to see 'tilt' of a square wave, the 3dB point of an AC couping stage has be be about
7 *times* lower than the frequency of interest.

The sound card probably has it's lower 3dB point set for voice, about 200Hz. This is why MOTM
demos recorded on SoundBlasters sound terrible.

If you aren't convinced, I'll fire up my 2Gs/sec digital scope with the 500Mhz probes :)

Paul S.

Mystery solved.  I admit to lying before: the output of the 300 was 
going into the 410 with MIX completely dry and MIX OUT to the 
console.  What's wrong with this picture, anyone?

:)

Feeling a bit dorky at the moment,

Mike

--- In motm@y..., "Paul Schreiber" <synth1@a...> wrote:
> You are observing a "hidden" HPF (high pass filter), caused by the 
reactance of the AC coupling

> network on the sound card.
> 
> ...

>Feeling a bit dorky at the moment,

The first time I saw the *output* from a sound card being used as a square
wave generator on a 'scope I thought "where are all the harmonics?--is
something acting like a resonating filter?" I switched to DC and it looked
the same, and then it hit me--low sampling rate.

This is the image that popped into my mind when I first read your post, but
as it happens it sounds like that's not what was happening in this case,
and Paul and Scott are probably dead on.
-- 

Terry Bowman, KA4HJH
"The Mac Doctor"

"It gets calls when nothing else works"--Walter Eugene Scott, PdD,
explaining somewhat facetiously why a "TV preacher" was smoking a cigar.

----- Original Message -----

From: "mmarsh100" <mmarsh@...>

> Mystery solved.  I admit to lying before: the output of the 300 was
> going into the 410 with MIX completely dry and MIX OUT to the
> console.  What's wrong with this picture, anyone?

hello all,
i did almost exactly the same thing last night - i was putting a freeware
tuner through it's paces (chromatia from www.fmjsoft.com) and wandered why
the tuner was going bananas...

...answer - i was using the output of the 420 VCF instead direct from the
VCO

cheers paul b
sheffield
uk

Well, AS THE MANUAL PLAINLY STATES (Paul told me to RTFM and I always 
follow his instructions to the letter) the input of the 410 is 
buffered by U2B then goes to U2A: "U2A forms a 65 Hz high-pass 
filter".

!!!

Now folks will see why I'm feeleing dorky,

Mike

--- In motm@y..., "mmarsh100" <mmarsh@s...> wrote:

> Mystery solved.  I admit to lying before: the output of the 300 was 
> going into the 410 with MIX completely dry and MIX OUT to the 
> console.  What's wrong with this picture, anyone?
> 
> :)
> 
> Feeling a bit dorky at the moment,
> 
> Mike
>