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PostPosted: 30 Oct 2008, 09:04 
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TestGuru wrote:
Would a sound card based oscilloscope/spectrum analyzer/signal generator be a better choice for audio test & measurement? The reason is that a good sound card can provide 192kHz sampling rate, 24 bit ADC and DAC, very good SNR, THD, IMD....which is essential for HIFI testing.

I just finished reading Morgan Jones "Building Valve Amplifiers" and in it he states that Sound Cards should never be used as oscilloscopes. According to Jones (see page 191) the bandwidth provided by the sound cards are not nearly enough.

Alan

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PostPosted: 10 Jan 2009, 04:41 
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gmilitano wrote:
You can use a soundcard and I have done so in the past. However, you need to build an accurate voltage divider network for it. I would also suggest putting in some voltage clamping for protection. A soundcard does not like more than about one volt.

What software package are you looking at?

There are quite a few good trialware available which provides many functions rather than just a waveform viewer and simple spectrum analyzer, they are:

1. Spectraplus at: http://www.spectraplus.com
2. Multi-Instrument at: http://www.multi-instrument.com
3. DSSF3 at: http://www.ymec.com
4. Sigview at: http://www.sigview.com
5. Visual Analyzer at: http://www.sillanumsoft.org
6. RMAA at: http://www.rightmark.org

Spectraplus seems to has the longest history. Multi-instrument can also work with a dual-trace 100MHz PC USB DSO unit in addition to sound cards and NI DAQmx cards, and a dedicated sound card oscilloscope probe is provided. Among these softwares, only Visual Analyzer is a FREEware as of now. Only Multi-Instrument and RMAA support ASIO sound card driver which is used widely in Pro-Audio industry.


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PostPosted: 10 Jan 2009, 05:07 
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TestGuru wrote:
Would a sound card based oscilloscope/spectrum analyzer/signal generator be a better choice for audio test & measurement? The reason is that a good sound card can provide 192kHz sampling rate, 24 bit ADC and DAC, very good SNR, THD, IMD....which is essential for HIFI testing.

booangler wrote:
I just finished reading Morgan Jones "Building Valve Amplifiers" and in it he states that Sound Cards should never be used as oscilloscopes. According to Jones (see page 191) the bandwidth provided by the sound cards are not nearly enough.

Yes, many sound cards have an analog bandwidth within 20Hz~20kHz, so it works within audio frequency only, and cannot measure DC, and will distort the square waveform in some degree depending on the square wave's frequency. Some good sound cards can work down to a few Hz, and up to 96kHz with a sampling rate of 192kHz and bit depth of 24. This should be enough for most, if not all, audio measurements.

IMO, for THD, SNR, IMD, Speech Intelligibility kinds of measurements in audio frequency range, a good sound card would be much better than a USB DSO with hundreds of Mega Hz sampling rate but has a bit depth of only 8 or 12. This is why the professional softwares (sold at "professional" price) such as clio, SMARRt and soundcheck use sound cards for audio measurements.


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PostPosted: 13 Jan 2009, 07:43 
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Location: iceland
Has anybody any experience or opinion on this Parralax USB Oscilloscope
Image

the specifications are:
  • 2 Channels
  • 1 Ms/s Maximum Sample Rate with One Channel
  • 500 Ks/s Sample Rate with Two Channels
  • 20 Vpp Maximum Input for Channel 1 and Channel 2
  • 200 kHz Bandwidth
  • 8-Bit Vertical Resolution
  • 1 M Ohm Input Impedance
  • Trigger on Rising or Falling Edge at any Voltage
  • Variable Trigger voltage on Channels 1 and 2
  • Horizontal Trigger Position Settings at 10%, 50%, and 90%
  • Auto and Normal Trigger Modes
  • 3 probes
  • USB 1.1 Support (no additional power supply required!)
  • Size: 5 x 2.25 x 1.5 (in.); 12.7 x 5.7 x 3.8 (cm)
  • Weight: 8 oz; 227 gm
  • Additional benefits: 14-day return for refund and 90-day workmanship warranty; free Parallax technical support by e-mail and phone; free software upgrades
it is selling for about $100, comparted to the dso which is about $200


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PostPosted: 13 Jan 2009, 18:17 
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kristfin, I have not tried that scope, but note that the bandwidth is only 200 kHz compared to 60MHz for the DSO-2150 which makes up the big price difference.

Rule of thumb, you want the bandwidth 3 times the analogue frequency you want to measure. Here is a good overview.
http://www.audiodesignline.com/showArti ... =201802022

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PostPosted: 25 Dec 2009, 23:13 
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Gio,

What do you use to generate your test signals?

Alan

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PostPosted: 26 Dec 2009, 02:02 
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Use a test CD. There are a lot you can download and burn. They have tones from DC to 20kHz. Dont play DC as you actually can play DC and if you are DC coupled... well you get DC on the speakers.
Uriah

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PostPosted: 28 Dec 2009, 18:37 
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Hi Alan, I recently got a TENMA low distortion signal generator. Prior to that I had an older generator, but I was never happy with the quality of the low and high frequency square waves.
Cheers

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PostPosted: 29 Dec 2009, 13:42 
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Gio,

Is this what you picked up?
Attachment:
72-455A.jpg
Or did you go with one of the hand helds? I have an old EICO that I was going to refurbish but that isn't happening for a while.

Alan


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PostPosted: 30 Dec 2009, 13:17 
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Hi Alan, yes, that is the one I got. Bruce has the same one and he is happy with it so I followed his lead.
Cheers

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