About a Diy pc oscilloscope found on the Net

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Useful oscilloscopes have knobs on.

But as was pointed out by I_Forgot, an oscilloscope that can only see audio is virtually useless for audio. There is no such thing as too much bandwidth - 20MHz is the absolute minimum and 100MHz is much better. Seriously, virtual oscilloscopes (PCs or Macs pretending to be oscilloscopes) are a waste of time and money. A decent 'scope is one that doesn't miss things and that is easy to use. Virtual oscilloscopes fail on both counts (and so do many digital "real" oscilloscopes). Buy a second-hand 100MHz Tek and be done with it.
 
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FastEddy said:
Holy Cow! an Apple Scope, free for the downloading!

It will stop at random times if not purchased but does give a good chance to try it. I mostly use mine for signal generator and speaker measurement (where its limited bandwidth is not a huge issue -- bandwidth is limited only by the I/O device and as those get wider bandwidth so does the scope)

dave
 
" ... bandwidth is limited only by the I/O device ..."

... same same with any 'scope software. A USB 16 bit / 48k, DAC / ADC would be limited to that 48k bandwidth and 16 bit resolution. Most 'puter 'scopes have 8 bit A to D convertrs but much broader resolution (bandwidth) ... so it would be a bad trade off for anything above audio range. I also noticed that several of the music recording software tools can display "oscilloscope like" graphics (like ProTools, etc.), also quite useful to audio types. But your link was the first I knew of this "shareware" 'scope software ... I like it. :D
 
Here is the circuit I've been using for several months now. I like it.
http://xoscope.sourceforge.net/hardware/hardware.html
Its basically a buffer to protect your pc. I use it with my modified soundcards for audio BW. It has much better sensitivity than any scope I've used, and is easier to read too...

I've found a couple of programs I like:
http://www.zeitnitz.de/Christian/Scope/Scope_en.html
This one is good for basic scope functions.

http://www.sillanumsoft.com/
This one does averaging and frequency analysis, which is nice.

Sometime I'm going to dive into rmaa:
http://audio.rightmark.org/index_new.shtml

-Patrick
 
FastEddy said:
" ... bandwidth is limited only by the I/O device ..."

... same same with any 'scope software. A USB 16 bit / 48k, DAC / ADC would be limited to that 48k bandwidth and 16 bit resolution.

Any digital sampling scope, including one that uses a computer sound card, requires some anti aliasing filter at the input to limit bandwidth of the signal hitting the DAC. A 48 ksps DAC would have a theoretical BW of 24 kHz, but a practical BW of 10-15 kHz due to the difficulties in making good sharp cut-off filters.

Not very useful...

I_F
 
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I_Forgot said:
Any digital sampling scope, including one that uses a computer sound card, requires some anti-aliasing filter at the input to limit bandwidth of the signal hitting the DAC.

As you say, it's needed. But it's not there. It's assumed that anyone having the money to buy an oscilloscope has a nodding acquaintance with Nyquist and will recognize aliasing when they see it. The reason oscilloscopes don't have an anti-aliasing filter is that it would have to change filter frequency to suit sample rate (which changes dependent on timebase setting and record length).

This lack of anti-aliasing filter and reliance on user-expertise is one of the reasons why I try to steer people away from digital oscilloscopes. You need a whole lot more knowledge to use a digital oscilloscope than an analogue...
 
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