Re: Modern Vector demo!

On Wed, 8 Aug 2007 12:23:32 +0200, "MyPearl" <mypearl@dds.nl> wrote:

>Well, that doesn't work then...
>
>Tried it on two tek scopes, so that should not be the problem.

Impressive demo!

My guess is the demo had to be carefully tuned to the soundcard in use.

If you search archived threads of vectorlist and RGVAC you'll see this was
discussed in some detail at one point.

As mentioned a soundcard has blocking caps that prevent it from holding a
position, and makes it hard to draw straight lines. If you place the trace
anywhere on the screen using a soundcard, it will quickly drift to the center of
the screen. To keep it centered you need to send vectors on both sides of the
center of the screen that average out to be the same X and Y voltages.

But beyond that, soundcards aren't designed to draw vectors, they output values
at a constant rate (44.1khz, which is pretty slow for vectors), and an output
filter is used to remove signals above 22KHz, or so.

The output filter is either capacitor based, or is functionally equivalent to a
cap, and if you send the proper output values you can let that filter circuitry
fill in the spaces between the dots, allowing you to draw vectors.

The problem is that there is no standard "filter", it just there to remove the
inaudible stuff that can ruin speakers, each filter will have a different slope,
and the tolerances can be really sloppy and yet have no effect on audio.

To do this right, you'd really need to "tune" your flac file to a specific brand
of soundcard, and possibly even a specific sound card.

There's no Z-axis on a sound card, I'm assuming he just jumps faster to the
start of a new vector, and slows down to fill in the vectors, and then adjusts
the o'scope's intensity to make the retrace lines invisible.

You can't use another channel of a sound card for a Z-axis since it also has a
blocking capacitor and would not be able to hold an intensity value or color. It
would always drift quickly to zero, not to mention it would send negative values
to the Z-axis of the monitor, which is not a good thing.

And knowing all that makes this demo even that much more impressive!

-Zonn

>----- Original Message -----
>From: "Frank Palazzolo" <palazzol@comcast.net>
>To: <vectorlist@vectorlist.org>
>Sent: Wednesday, August 08, 2007 3:32 AM
>Subject: Re: VECTOR: Modern Vector demo!
>
>
>> MyPearl wrote:
>>> Another problem I noticed (and expected) is that the soundcards
>>> output is AC coupled and therefore the center of the image
>>> on the scope drifts in both x and y direction. Maybe I need
>>> to chop up an old soundblaster just for this demo :)
>>
>> It appears he is offsetting the beam to the four corners of the display
>> for certain amounts of time, probably to add the proper "DC offset" via AC
>> components. I think this must be how he gets around this limitation of
>> sound cards. Otherwise, I can't see how an arbitrary AC-coupled audio
>> signal could work.
>>
>> This is quite an amazing piece of work - both the demo and this technique.
>>
>> -Frank
>> ---------------------------------------------------------------------------
>> ** Unsubscribe, subscribe, or view the archives at
>> http://www.vectorlist.org
>> ** Please direct other questions, comments, or problems to
>> chris@westnet.com
>>
>>
>> --
>> No virus found in this incoming message.
>> Checked by AVG Free Edition. Version: 7.5.476 / Virus Database:
>> 269.11.6/938 - Release Date: 5-8-2007 16:16
>>
>>
>
>---------------------------------------------------------------------------
>** Unsubscribe, subscribe, or view the archives at http://www.vectorlist.org
>** Please direct other questions, comments, or problems to chris@westnet.com
---------------------------------------------------------------------------
** Unsubscribe, subscribe, or view the archives at http://www.vectorlist.org
** Please direct other questions, comments, or problems to chris@westnet.com
Received on Thu Aug 9 19:22:33 2007