Calibrated distortion source???

Zero Cool · 3rd October 2008, 04:39 PM

I am looking for a way to build a device with a know amount of distortion for testing my HP 339A. Something with 1%, 3% 10% doesn't matter as long as it is a known amount.

How would I do that??

sreten · 3rd October 2008, 05:10 PM

Hi,

Things like square waves, sawtooth, triangular all have fixed
high levels of distortion, the values I do not know offhand.

But you could simply mix two known signals together
with one representing the distortion could you not ?

/sreten.

scott wurcer · 3rd October 2008, 05:15 PM

I made them in Audition (Cooledit) and burned them onto a CD (not these exactly but other test waveforms).

Zero Cool · 3rd October 2008, 07:08 PM

Yeah i have ways to create waveforms including sig gens and soundforge etc, but nothing where i can create a device or a signal with a know about of distortion.

I would like to build a box. some form of op-amp device with a way to create a precise amount of distortion.

Zc

wakibaki · 3rd October 2008, 07:44 PM

Here is a distortion meter/signal generator. You should be able to create signals with a measured amount of distortion, if only by trial-and-error.

w

You can create a signal with arbitrary distortion characteristics by calculation. Values can be created in Excel, for example, for a pure sampled sine wave, which can have a harmonic added at a lower amplitude. Then the values can be turned into a .wav file and played back. Figuring out how to do this is almost as interesting as playing with opamps.

Zero Cool · 3rd October 2008, 08:18 PM

Hmmmm, I have a HP 339A distortion analyzer but i need to check how accurate it is.

Hardi · 3rd October 2008, 09:40 PM

The 339 measures always THD+noise and not THD. You can exclude high and low frequency noise with the build in HP & LP filters, but that will not lead to an exact calibration.
The THD level of a squarewave also depends on its exact 50/50 duty cycle and a very fast rise time.
A good & cheap way may be any analyzer-software like Specralab as a reference, but the noise problem is still present.

Hardi

jcx · 4th October 2008, 12:27 AM

http://www.diyaudio.com/forums/showt...21#post1178021

and others in that thread use LtSpice to create .wav files with known components

jackinnj · 4th October 2008, 12:46 AM

how about this

wakibaki · 4th October 2008, 05:46 PM

Ideal, jacknnj

You can send the fundamental out your L channel and the harmonic out the R channel.

However real world distortion is never just in 1 harmonic. But then I guess it's just a ballpark test for a meter.

I'd still just combine the signals somehow in the digital domain, and play the result back thru a single channel of a good DAC. Less hardware, less problems.

w

3rd October 2008, 04:39 PM	#1
Zero Cool Audio Junkie diyAudio Member Join Date: Sep 2004 Location: MN	Calibrated distortion source??? I am looking for a way to build a device with a know amount of distortion for testing my HP 339A. Something with 1%, 3% 10% doesn't matter as long as it is a known amount. How would I do that??

3rd October 2008, 05:15 PM	#3
scott wurcer diyAudio Member Join Date: Jan 2004 Location: cambridge ma	I made them in Audition (Cooledit) and burned them onto a CD (not these exactly but other test waveforms). __________________ Pain is never permanent

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3rd October 2008, 05:10 PM	#2
sreten diyAudio Member Join Date: Nov 2003 Location: Brighton UK	Hi, Things like square waves, sawtooth, triangular all have fixed high levels of distortion, the values I do not know offhand. But you could simply mix two known signals together with one representing the distortion could you not ? /sreten.

3rd October 2008, 07:08 PM	#4
Zero Cool Audio Junkie diyAudio Member Join Date: Sep 2004 Location: MN	Yeah i have ways to create waveforms including sig gens and soundforge etc, but nothing where i can create a device or a signal with a know about of distortion. I would like to build a box. some form of op-amp device with a way to create a precise amount of distortion. Zc

3rd October 2008, 07:44 PM	#5
wakibaki Banned Join Date: Jan 2008 Blog Entries: 2	Here is a distortion meter/signal generator. You should be able to create signals with a measured amount of distortion, if only by trial-and-error. w You can create a signal with arbitrary distortion characteristics by calculation. Values can be created in Excel, for example, for a pure sampled sine wave, which can have a harmonic added at a lower amplitude. Then the values can be turned into a .wav file and played back. Figuring out how to do this is almost as interesting as playing with opamps.

3rd October 2008, 08:18 PM	#6
Zero Cool Audio Junkie diyAudio Member Join Date: Sep 2004 Location: MN	Hmmmm, I have a HP 339A distortion analyzer but i need to check how accurate it is.

3rd October 2008, 09:40 PM	#7
Hardi diyAudio Member Join Date: Feb 2004 Location: Germany	The 339 measures always THD+noise and not THD. You can exclude high and low frequency noise with the build in HP & LP filters, but that will not lead to an exact calibration. The THD level of a squarewave also depends on its exact 50/50 duty cycle and a very fast rise time. A good & cheap way may be any analyzer-software like Specralab as a reference, but the noise problem is still present. Hardi

4th October 2008, 12:27 AM	#8
jcx diyAudio Member Join Date: Feb 2003 Location: ..	http://www.diyaudio.com/forums/showt...21#post1178021 and others in that thread use LtSpice to create .wav files with known components

4th October 2008, 05:46 PM	#10
wakibaki Banned Join Date: Jan 2008 Blog Entries: 2	Ideal, jacknnj You can send the fundamental out your L channel and the harmonic out the R channel. However real world distortion is never just in 1 harmonic. But then I guess it's just a ballpark test for a meter. I'd still just combine the signals somehow in the digital domain, and play the result back thru a single channel of a good DAC. Less hardware, less problems. w

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