tone generator frequency

[kurtlastdays]

Hi!

I need answers on a theoretical question.

Suppose I build a tone generator that produces a sound of 100Hz frequency, and another one of 150Hz frequency.

Now, if I combine this two in the same output source, what frequencies will I be getting?

Someone told me it is 100, or 150, or 50, or 250.
Is this true?

:?

 

[JimB]

It all depends on what you mean by combine.
If the device doing the combining is linear, (produces no distortion), you will have 100hz and 150hz, the same as you put in.

However, if the device doing the combining is non-linear, you can get all sorts of things:
100, 200, 300, 400...etc
150, 300, 450, 60...etc
This is called harmonic distortion.


100+150=250, 150-100=50 2x250-100=400, 3x250-2x100=550, etc etc.
This is called intermodulation distortion.

It can get quite messy.

JimB

 

[kurtlastdays]

It all depends on what you mean by combine.
If the device doing the combining is linear, (produces no distortion), you will have 100hz and 150hz, the same as you put in.

However, if the device doing the combining is non-linear, you can get all sorts of things:
100, 200, 300, 400...etc
150, 300, 450, 60...etc
This is called harmonic distortion.


100+150=250, 150-100=50 2x250-100=400, 3x250-2x100=550, etc etc.
This is called intermodulation distortion.

It can get quite messy.

JimB

Ok, assuming I have the following tone generator:

http://www.solorb.com/elect/hamcirc/sidetone/

I have 2 of them, "tuned" into 2 distinct frequencies.

I want to insert them into an audio PC card.

What should I do (i.e a schematic to "linear" combine them) to have into my PC's card only the 2 frequencies (no distortion of either kind) :?:

Help appreciated!

 

[audioguru]

That circuit produces a sine wave with audible distortion, since it uses only a two stage filter for its triangle wave. Its VCA also adds distortion. There is an additional integrator which won't reduce the distortion much, since if it did, it would also reduce the fundamental frequency.
If you need low distortion sine waves, why not use a low distortion sine wave oscillator? :?:

Tones can be combined without additional distortion by adding them with a resistor from each then joined at the input. If one tone must remain on while the other turns on and off, an inverting opamp must be used as a summer for complete isolation of the levels of the two tones. :lol:

 

[JimB]

That oscillator was designed for a very specific purpose and may be a lot of overkill or totally inappropriate for your application.

What are you trying to achieve by feeding two tones into your PC sound card?

JimB

 

[robo-cop]

Thank you for the answers.

I try to do the following:

the audio enters the PC audio card and there is a software inside my PC which executes a certain command when a certain audio frequency enters the audio card.

There are about 20 commands I want to be able to execute by the use of 20 different audio frequencies.

So, I am looking for a "one-frequency" oscillator, I want to build 20 of those with distinct frequency each,
connect them all together into a box and feed them into a line-in of a PC audio card.

Also, assuming intermodulation distortion cannot be entirely eliminated, could I set frequencies in way that:
when 2 or more oscillators trigger together, their intermodulated frequencies do not develop a frequency identical to the main frequency of another oscillator?

Thanx.

 

[audioguru]

Distortion of the tones won't matter if the tone detectors have strict amplitude settings. The circuit you showed might have only (!) 5% distortion.
It sounds like you are trying to re-invent touch-tone (DTMF) which responds to only 12 combinations of non-combining frequencies.

 

[JimB]

Dont get too worried about intermodulation distortion, I am sure it will not be a problem in this application.

To save re-inventing the wheel, have a look at DTMF as Audioguru suggests, it can signal 16 different states.
Look here https://en.wikipedia.org/wiki/DTMF to get started.

JimB

 

[audioguru]

Touch-tone has 16 states?
Oh yeah, my phone has only 12 but I forgot about A to D.

 

[Dr.EM]

Wouldn't a far simpler square wave generator be more suitable for this? All that filtering and voltage controlled amplifier certainly seems uneeded. I know that the square waves have lots of harmonics, but isn't the system that recognises them just like a digital counter anyway?

 

[kurtlastdays]

Dont get too worried about intermodulation distortion, I am sure it will not be a problem in this application.

To save re-inventing the wheel, have a look at DTMF as Audioguru suggests, it can signal 16 different states.
Look here https://en.wikipedia.org/wiki/DTMF to get started.

JimB

The thing is, these things are of constant amplitude, right?

I want mine to be of variable amplitude, can it be done? :wink:

Thanx!

 

[audioguru]

If the frequency detector is just a digital counter then amplitude doesn't matter much. If it has tuned circuits then an automatic gain control circuit could be added.
EDIT: Wait a minute! A digital frequency counter can't have more than one frequency at a time.

 

[Nigel Goodwin]

The thing is, these things are of constant amplitude, right?

I want mine to be of variable amplitude, can it be done? :wink:

Perhaps you should try explaining EXACTLY what you are trying to do?, it doesn't sound very practical?.