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Old 11th March 2013, 07:35 PM   #11
xstreme is offline xstreme  Europe
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Compared Tolvan and Tgen...

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Last edited by xstreme; 11th March 2013 at 07:53 PM.
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Old 12th March 2013, 02:32 PM   #12
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@ geraldfryjr

would be interesting to compare various audio generator waveforms , with detailed technical evaluations of an expert , who better than you ?
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Old 12th March 2013, 04:09 PM   #13
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Yes, this is something that has crossed my mind several times.
In the past I have found some that perform better than others and I was quite surprised by this.

I have seen some with great UI's and performed terribly and some that produced a great signal with very little to offer in the form of control over the signal.

I don't have a standalone THD analyzer to do a proper comparison.
Although I do have three good quality sound cards to work with and every one of them produces a better signal than my standalone signal generator.
Except of course when it comes to square waves.
Nothing beats a good ole discrete switching circuit when it comes to those.

I was just thinking last night how I have been wanting and really need to build a signal generator for audio that will give a stable programable frequency resolution of at least .1 hz and even .01 hz.

I know that there are some software versions that do or may allow this but typically I have found that they are usually off by a certain small percentage or don't allow for a full small step such as 1/10th or 1/100th of a hertz as this has to do with being a fraction of what the sample rate would allow.

I will consider this study sometime in the future as right now I have my head buried in coming up with a good DIY ESL step transformer.


Cheers !!!

jer
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Old 12th March 2013, 05:19 PM   #14
xstreme is offline xstreme  Europe
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Quote:
Originally Posted by geraldfryjr View Post
I will consider this study sometime in the future as right now I have my head buried in coming up with a good DIY ESL step transformer.


ESL : damn bias
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Old 12th March 2013, 07:43 PM   #15
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Quote:
Originally Posted by geraldfryjr View Post
Yes, this is something that has crossed my mind several times.
In the past I have found some that perform better than others and I was quite surprised by this.

I have seen some with great UI's and performed terribly and some that produced a great signal with very little to offer in the form of control over the signal.

I don't have a standalone THD analyzer to do a proper comparison.
Although I do have three good quality sound cards to work with and every one of them produces a better signal than my standalone signal generator.
Except of course when it comes to square waves.
Nothing beats a good ole discrete switching circuit when it comes to those.

I was just thinking last night how I have been wanting and really need to build a signal generator for audio that will give a stable programable frequency resolution of at least .1 hz and even .01 hz.

I know that there are some software versions that do or may allow this but typically I have found that they are usually off by a certain small percentage or don't allow for a full small step such as 1/10th or 1/100th of a hertz as this has to do with being a fraction of what the sample rate would allow.

I will consider this study sometime in the future as right now I have my head buried in coming up with a good DIY ESL step transformer.


Cheers !!!

jer
Just watch e-bay for an HP or Wavetech. You should find something for under ten grand.
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Old 12th March 2013, 08:06 PM   #16
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Ahhh,ha,ha,ha,ha,ha!!!!!

A 5Ghz scope would be nice!!!!!!

jer
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Old 12th March 2013, 08:40 PM   #17
tvrgeek is offline tvrgeek  United States
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A software generator is only as good as the systems clock at best. Pro studio stuff you can sync with a rubidium clock. They are only about $1600.

.01Hz. Is that at 1Hz, so 1% accurate or at 20Khz? You are not going to do better than a couple of Hz at 20K unless you greatly up the sample rate. You could do this with an external high speed clocked D to A. Make it USB as you are only sending control signals to it.

In reality, how good does it need to be for audio work? You may have a idea I have not thought about, but I can't imagine what you would need resolution below 1% in frequency. Low distortion and a constant amplitude are probably more important, and harder. Using a full 24 bits and 96K would help. Most freeware tools are 16 bit and 48K. 192? right. Of course, unless you have an analog preamp to deal with the amplitude, the 24 bit goes away real fast right along with the low distortion. Maybe a pure sine wave would integrate OK at lower resolution if your sound card has teflon caps in it.

What might be cool is a way to calibrate it. Say put out a 10K tone and hook up a counter. Enter the reading and let the software figure out the adjustment. Do it again at 100Hz to be sure it scaled. Same thing on the amplitude. Output at 60 Hz ( so a DVM can measure it) and enter the actual at-load. A sound card has a pretty high output impedance though, not like a good bench generator.
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Old 13th March 2013, 12:39 AM   #18
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in this time i'm rewriting my free area web site, but in next days will avaiable a new version of Sound Compiler, in the ranges i have added very low frequency sss
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Old 13th March 2013, 02:39 AM   #19
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Most likely a resolution to 1Hz would be good enough for most work.
But to at least to 1/10 would be nice.

You can enter in values to the 1/100 in VA but I have no way of verifying its accuracy as my frequency counter is only good to 1Hz resolution.

Wave spectra's signal generator and Tolvan data's has a very fine adjustment of the frequency and I like this and I can see the results using my scope.

But if try to use VA to verify this the best can get it to work is about 1.5Hz resolution or so and the display gets stuck while the frequency is some where in between.
The only other options are some odd numbers as .73, .37, .18 or .092 hertz increments and rarely can I get one of these ranges to work.

I guess it is just that my Cheapy meter has gotten me so mad that I realize that it is not that hard to build your own test equipment that has a decent amount of precision to it for the cost of a real good and decent meter.
Especially if you have the parts needed lying around in your parts bin for many years as I do.

If I can come up with a variable 0V to 13.8KV bias supply with control over the voltage of better than 1volt of resolution in one continuous range it can't be that hard to do.

In fact I just found my old XR2206 signal generator board that I built ages ago and all I need to do is add a PLL and some divider's.
I even found my ICL8038 chip should I want triangle waves with a variable duty cycle.
Even these are good but it is hard pressed to beat the low THD of a 24bit 192Khz sound card.

When you using the stuff to measure the values of components the resolution is a big deal especially at the lower frequency's.

At 100hz if your off by 5Hz are calculated values will be off by 5% plus what ever the tolerance of the part may be.
At 50Hz this would mean 10% and this could be a big deal depending on what you are working on or trying to do.

For instance the other day I was measuring some core saturation points on a transformer and when I got to 330hz everything was looking okay and by the time I got to 327hz the core was in complete saturation.
This is a only difference of .9% shift in the frequency.

VA has been a god send when it comes to measuring voltages at different frequency's as well.
But you must use an input buffer as the input impedance to the sound card changes with frequency and loads the circuit you are trying to measure differently giving you the same false reading as your typical cheapy DVM will do.

This is not good when you are trying to work in audio and when your meter says 1volt at 60hz is coming out of your amplifier and then .5V when you shift up to 1Khz or 10Khz when your scope clearly shows that the level has not changed and is in fact still 1Volt!

Depending on your scope you may not be able to get a voltage measurement accuracy of better than 10% and thus the need of some type of reliable measuring tool or system.
So far the software tools are working very good for me in this aspect.

For D.C measurement I am going to have to build an A/D interface eventually.
My recent attempts to bypass the input capacitor on the sound card has failed.
The input pins have there own D.C bias on them and the inputs will only respond to A.C. levels.
Even if I shift the DC bias with another voltage or by dragging it down with a resistor it self centers on the VA display while the input DC voltage doesn't change and still only responds to an AC signal.
However I have been able to get to about 1hz or less but it always self centers when the level is not changing.
I had got some extremely clean 10Hz and lower square waves into the input of the PCM chip by using a larger input capacitor but it was still only AC.

jer

Last edited by geraldfryjr; 13th March 2013 at 02:44 AM.
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Old 13th March 2013, 09:47 PM   #20
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"Most likely a resolution to 1Hz would be good enough for most work.
But to at least to 1/10 would be nice."

1Hz at 1Hz is 100%, at 20KHz it is .005%, which you are not going to do with a 48K sample rate let alone clock jitter.

Generating a signal is not the same as measuring it and displaying a value. Remember in digital signals processing, there is nothing between the points. THat requires the integrator and anti-aliasing filters.
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