High, Mids, Low. How it looks on the oscilloscope?

Stompboxes circuits published in magazines, books or on DIY electronics websites.
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piod
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Post by piod »

Please help me find the information. What would look a signal of "good taste" on the oscilloscope screen.
I realized that the waveform should be "sexy" without any distortions. But I'm confused with the experiment. We can adjust our pedals by ear, but oscilloscope screen can give a more precise answer.

I want to know where to go, where is true.

For example images waveform:
-high, and medium frequency
-mids
-cutting out the middle
-middle, high, Low

I am trying to set good tone of baxandall tone stack and it would be very help me.

Thank you guys and I apologize for my English. :roll:

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jymaze
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Post by jymaze »

Don't understand your question. If you feed different frequencies to the tone stack one by one, then you can see how much is left at the output on your oscilloscope, that is it. You cannot test all frequencies all at once with white noise and analyze the output on the oscilloscope with your eyes, it just looks like a mess! A computer can do it and extrapolate the frequency response though.

In a nutshell: Trust your ear, it is the only thing in the world that can tell you if things sound good or not.

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Post by Fender3D »

o-scope alone will show you just the voltage gain on the single applied frequency...

You'd better need:
a o-scope with xy capabilities,
a sine sweep generator,
a freq. counter

otherwise a low frequency spectrum analyzer.

You won't see a "signal good taste" on o-scope unless you look for a heavy distorted waveform...

When you're building tone controls, tone stacks or similar circuits, you're looking for filters working on several frequencies then the need for the sine sweep generator.
You should learn how measuring phase with o-scope, 'cause phase distortion will impact your sound severely.
Then you will look for the boundaries of your filters, then the need for the f. counter.

Not an easy reply, I know... but not an easy question also...

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piod
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Post by piod »

I apologize for some of the details. I work with a distorted signal. I have the oscilloscope and a sine wave generator, my set up 440 Hz, 0.5 volts.
The circuit gain gives an almost rectangular shape, and it goes to the tone-stack, that I'm looking shape.
Is it possible to configure this way? I'm analyzing a few pedals, the output have various forms.

Image
Image

Low on max, Mid and High min.

Image

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Post by mictester »

piod wrote: I am trying to set good tone of Baxandall tone stack and it would be very help me.
You're using the wrong instrument. An oscilloscope won't tell you much. You need an audio spectrum analyser and a white noise source. Feed the white noise into the tone control stage, and observe the output of the tone control circuit on the analyser. Adjust the controls, and you'll clearly see the shapes of the responses produced. You can then try substituting different capacitors and see how the response changes. This is how I do it (and most professional designers).

A spectrum analyser is also useful for checking the harmonic content generated by various different distortion circuits. You'll find that even harmonic content sounds nicer than odd, and tends to be the type of distortion produced by valve amplifiers. The non-linear characteristic each kind of stage is fascinating to see - diodes to ground produce large amounts of odd harmonics (and some even) and tends to sound harsh. Diodes in a feedback loop (like a Tube Screamer) produces a higher proportion of even order harmonics, so sound smoother.

Unfortunately, a spectrum analyser isn't as cheap as an oscilloscope!
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Post by Lucifer »

You might also want to look at the free Tone Stack Calculator at: http://www.duncanamps.com/tsc/

This allows you to alter components in various tone stack configurations, and you can see the resulting frequency response curves on screen.
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Post by jymaze »

Yep, look at white noise with an oscilloscope is pointless. There may be some cheap spectrum analyzer software though that could help you.

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Post by piod »

I found something interesting but in Russian
http://radio-gl.narod.ru/remont/osc/osc.htm

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Post by phatt »

Hey piod,

My guess is you are confusing waveform (Transient Analysis) with Frequency response curves (Bode plots).

Sure scopes are handy but you can save yourself a whole lot of trouble if you Dload and learn to use Sims. LT spice seems to be rather clever and cheap. :thumbsup

For the purposes of pedal builds don't waste time with hardware, only worth it if you plan on a whole career in Electrical Engineering.
my 2 cents,, Phil.

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Post by jimiguitar »

i found this software on ebay i'am wondering how i have a e-mu 1820m as my sound card it has smpte its a very high end sound card i'am wondering if this would work good i guess at that price it might be worth the try http://thumbs3.ebaystatic.com/d/l225/m/ ... QGwGfg.jpg

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Post by phatt »

Hi jimiguitar,
I'd not waste time on that as anything that uses a sound card is a toy (very limited bandwidth) :(
If you want to go in that direction expect to pay up to $1,000 for the hardware interface. :shock:

I'm just meaning simulation software that is cheap (some free) for the simple purpose of getting a basic idea of how the circuit works.
For hobby guys who just want to build a few simple audio circuit bitz it's all you need. :thumbsup

But hey you buy it let us know how it works out.
Phil.

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Post by jimiguitar »

i was just wondering about it and my sound card was not a toy it cost me 700 dollars its for professional recording it cam 14 tracks separate recording at the same plus it has a smpte clock for syncing music to films and its expanable

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Post by deltafred »

jimiguitar wrote:i was just wondering about it and my sound card was not a toy it cost me 700 dollars its for professional recording it cam 14 tracks separate recording at the same plus it has a smpte clock for syncing music to films and its expanable
It's all about how fast it will sample. If you can use one channel and sample it several times faster than when using all channels then it will probably make an acceptable scope as long as the software is up to the job.

Normal PC sound cards have way more resolution (bits wide) than a scope needs but are very limited in sample speed. The result of this is that they will give misleading results as the frequency rises. A scope needs a lot less bits wide but way higher sampling speeds.
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Post by phatt »

Thanks for the clarification *Deltafred* sounds like you have a deeper understanding of this but I've been warned by a reputable source to not waste time with the average soundblaster card because for serious analysis you need much more.
Plus you can't measure floating Voltage because the computer is grounded,, or something along those lines. :scratch:

And sorry *jimiguitar*, my brain faded and I was giving a rather generalized answer. :oops:
But yep at $700 it may well do what you need. :thumbsup
Phil.

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Post by jimiguitar »

it has capable of 192khz i was wondering about spectrum analyzers and frequency counters i already have dedicated oscilloscopes, function generator, just wondering how good the results would be using my computer thats all as frequency counter and spectrum analyzer thats all since i'am coming into some money just want to be able to do more at the bench trouble shooting and building thanks to everyone for the useful information seems like i always just somethings but not enough thank you

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Post by DrNomis »

piod wrote:I apologize for some of the details. I work with a distorted signal. I have the oscilloscope and a sine wave generator, my set up 440 Hz, 0.5 volts.
The circuit gain gives an almost rectangular shape, and it goes to the tone-stack, that I'm looking shape.
Is it possible to configure this way? I'm analyzing a few pedals, the output have various forms.

[ Image ]
[ Image ]

Low on max, Mid and High min.

[ Image ]


From looking at the scope screenshots you posted, the top one shows what happens to the waveform if you scoop out the mids, the middle screenshot shows what happens to the waveform if you boost the highs, and the bottom screenshot shows what happens to the waveform if you cut the highs and boost the lows..... :thumbsup


To see the frequency response of the tone controls, you really need to use a Spectrum Analyser, this is one of the functions of Digital Storage Scopes..... :thumbsup
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Post by deltafred »

The flash analogue to digital converters (A/D) used in scopes are very different to the successive approximation used in sound cards. Flash A/Ds that have a lot less bits but are orders of magnitude faster. A successive approximation A/D makes a poor scope and flash a A/D makes a poor audio sampler.

The more sample points per cycle you have the better accuracy you have for data analysis as long as you have sufficient resolution (number of bits). It has been a long time since I worked on instrumentation and have forgotten a lot of the theory. If you are interested read up on data acquisition, processing and analysis (if you can get your head round the maths, something I usually struggled with).

For performing spectrum analysis you want a lot of sample points per cycle because the distortion introduced with too few points will skew the results (introducing frequency components that are not actually there and ignoring or attenuating others that are).
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Post by mganzer »

Is possible to use a pc (vst) based fft audio spectrum analizys for this?
After some search i found this: http://www.nugenaudio.com/spectrum-analyzer_VST_AU.php and this: http://www.bluecataudio.com/Products/Pr ... lystMulti/, of couse limited by the input/output device... I found some apps for android and ios but seems to have some lag.
So what the procedure? input some white noise in the circuit and record to use an spectrum analyzer over the record?

Thanks.

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Post by chicago_mike »

Cubase. I would use the exact same card you have. E-MU 1820M. Run it thru Cubase or Samplitude.

But I was using these to run signals through my pedal builds. To trace signals and such. You could get Freq response out of them as well. At least Samplitude had the style of metering you are thinking of.

Cubase has s signal generator. You could set it up on a track and run it from 20 to 20k in increments. You could also setup multiple tracks with signal generators and test multiple freq's at a time through your diy build.

It's how I trace my builds for signal routing, and issues. Works great. :)
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