Square wave through sound card.

[carulli2]

I recently purchased an oscilloscope and just to test it out I made a square wave at 1000hz with audacity and displayed it through the cro. The output is shown in the video, not sqaure at all but I do see it is trying to be. My question is, is this because audacity cant make a proper square wave (I dont think so but maybe), is it because mt cro cant handle it (i doubt that too) or is it because my sound card is a failure when it comes to outputting square waves?

also notice how for the first second of output there is a fade from a better SW to the poor SW then i shift to the left. why is this?

the cro is a BWD model 502 (old Australian model form the 60s lol).

 

[Bionic-Badger]

I can't tell what scale your oscilloscope is working. Most soundcards have output filters on them to reduce noise and other things and that could affect your square wave's shape. If you want something squarish, you'll need to increase the wavelength of the base square shape. So for example, most square waves in music are at low frequencies, like 180hz or something, so that the upper frequencies can "construct" the sharp transition. At 1khz, you may not have enough bandwidth to make a really sharp transition.

Also make sure you're doing DC coupling on the probe.

 

[carulli2]

well it turns out it was my sound card. using a function generator (freqgen) on my iphone produces nice clean waves. kind fun to pay around with actually, really helps you learn which settings so change in order to get a nice wave on the screen.

 

[Things]

Most soundcards have decoupling capacitors on their outputs that like smoothing out square waves. That's why they are bypassed when using soundcards as DAC's.

 

[Bionic-Badger]

Another thing to check for, and this affects laser soundcard DACs, is to be sure that all the channels on the output of your sound card are independent. Some sound cards mix the channels especially if you don't have a full surround sound system, but want a "surround sound" sound.

If that is the problem, here is how you can set it up (at least with a CMedia sound card).

 

[carulli2]

I'm 100% sure my pc does have that enabled. On another note, I should receive the rest of the parts needed for the circuit I'm building so I should be able to test a nice sqare wave without ringing. Ill let you guys know.

 

[Benm]

There is no way a 1 kHz square wave should be output that badly by a soundcard unless it has some effects (equalizer etc) enabled. You would expect to see slightly rounded edges and perharps very minor deformation of the horizontal lines, but nothing like this.

The rounding is normal at caused by both the limited sample rate of the soundcard and the anti-aliasing filter.

 

[Bionic-Badger]

That channel mixing really messes up soundcard DAC outputs. The image is doubled and phase shifted, so that distorted images appear diagonally from the center on the X/Y axes.

 

[Benm]

I have no idea whats going on with this soundcard, but if a square wave comes out like that i doubt it will sound very good. Perhaps it uses phase shifting though the spectrum and the result wouldn't be that bad, but that makes me wonder why anyone would do that on a soundcard for home use.