mixing waveforms... like for a synthesizer

[panfilero]

This may be a really simple question, but I was wondering what is the
correct way to mix 2 or more waveforms. For example if I want to mix
a sine wave and a sawtooth wave in order to produce an audio tone.
So, lets say I have a sine wave of a a few millivolts and a sawtooth
of about the same amplitude and nearly the same frequency and both of
them are signals which can independently drive a little speaker... but
now I would like to mix the two signal and listen to the resulting
signal. If both of those signals are the outputs of two different
pins or wires... do I just connect the two wires together? I don't
think that's the right way to do it for some reason... but I'm not
sure what is.

Thanks

 

[Michael Black]

This may be a really simple question, but I was wondering what is the
correct way to mix 2 or more waveforms. For example if I want to mix
a sine wave and a sawtooth wave in order to produce an audio tone.
So, lets say I have a sine wave of a a few millivolts and a sawtooth
of about the same amplitude and nearly the same frequency and both of
them are signals which can independently drive a little speaker... but
now I would like to mix the two signal and listen to the resulting
signal. If both of those signals are the outputs of two different
pins or wires... do I just connect the two wires together? I don't
think that's the right way to do it for some reason... but I'm not
sure what is.

But what are you trying to do?

Create a signal with two different sounds, or create a different sound?

The first is simple "mixing". Just like in a recording studio, where
they have multiple microphones and sound sources (from electric instruments),
and they are mixed together to get the total sound. IN that case, they
are just summed together. The usual thing is a an op-amp configured as
an inverting amplifier, and then instead of one input resistor, there
are multiple resistors, one for each sound source. Usually, there is a pot
before each of those resistors, so the sound level of each "channel" can
be adjusted.

If you are trying to create a new sound, then you need something more
complicated. But keep in mind that in analog synthesizers, the usual
method is to start with a sawtooth waveform, and then filter to get the
right waveform. Or pick the an appropriate waveform, square, pulse or
maybe triangle, which may make the actual adjustments simpler.

Digital changes it all.

But if you are creating a new waveform, the output will not contain
the two original waveforms, and you can't simply "mix" them together
like in the first case.

Explain what you really want, and you'll get an answer.

Michael

 

[panfilero]

But what are you trying to do?

Create a signal with two different sounds, or create a different sound?

The first is simple "mixing". Just like in a recording studio, where
they have multiple microphones and sound sources (from electric instruments),
and they are mixed together to get the total sound. IN that case, they
are just summed together. The usual thing is a an op-amp configured as
an inverting amplifier, and then instead of one input resistor, there
are multiple resistors, one for each sound source. Usually, there is a pot
before each of those resistors, so the sound level of each "channel" can
be adjusted.

If you are trying to create a new sound, then you need something more
complicated. But keep in mind that in analog synthesizers, the usual
method is to start with a sawtooth waveform, and then filter to get the
right waveform. Or pick the an appropriate waveform, square, pulse or
maybe triangle, which may make the actual adjustments simpler.

Digital changes it all.

But if you are creating a new waveform, the output will not contain
the two original waveforms, and you can't simply "mix" them together
like in the first case.

Explain what you really want, and you'll get an answer.

Michael

OH, I didn't know that it was different... I would like to create a
new sound out of the mixed waveforms (am I wrong to use the words
waveforms and signals interchangeabley?) I was thinking that mixing
the two signals would output a new different signal that would be the
sum of the original two signals....

When you mention sending them to an op-amp, are the two signals mixed
at the inverting input of the op-amp? And the opamp then just
amplifies the already mixed signal?

Thanks

 

[BobG]

The word 'mixing' means 'arithmetic addition' to audio guys and
'multiplication' to rf engineers. When you multiply two sine waves,
you get the sum and difference of the two waves (carrier freq and
modulation in rf language). If one of them has harmonics like a
sawtooth, the product is the sum and difference of all the harmonics
in each wave. Real complicated and usually sounds like dogbreath.
Unfortunate overloading of an otherwise perfectly descriptive term.

 

[[email protected]]

sound?






OH, I didn't know that it was different... I would like to create a
new sound out of the mixed waveforms (am I wrong to use the words
waveforms and signals interchangeabley?)   I was thinking that mixing
the two signals would output a new different signal that would be the
sum of the original two signals....

When you mention sending them to an op-amp, are the two signals mixed
at the inverting input of the op-amp?  And the opamp then just
amplifies the already mixed signal?

Thanks

So go on eBay and pick up Cool Edit pro 2.0 and do all the mixing in
the PC. Saves scads of time as you don't build anything, just use what
you already have and works an order of magnitude better and for less
money. Plus you can chorus, reverb, equalize, noise reduce, change
pitch and MUCH more. You would not regret buying it.

Adobe bought out Syntrillium and renamed it Audition

GG

 

[Jon Slaughter]

This may be a really simple question, but I was wondering what is the
correct way to mix 2 or more waveforms. For example if I want to mix
a sine wave and a sawtooth wave in order to produce an audio tone.
So, lets say I have a sine wave of a a few millivolts and a sawtooth
of about the same amplitude and nearly the same frequency and both of
them are signals which can independently drive a little speaker... but
now I would like to mix the two signal and listen to the resulting
signal. If both of those signals are the outputs of two different
pins or wires... do I just connect the two wires together? I don't
think that's the right way to do it for some reason... but I'm not
sure what is.

You need a mixer. You can do this simply with an op amp or some various
other methods.

The op amp method is nice and easy and lets you add any number of sources
into one and you can easily control how much by changing the resistors(so
you would want to use pots).

http://homepages.which.net/~paul.hills/Circuits/Adder/Adder.html

That site shows the idea.

Note that you cannot simply short the pins together and get what you want
cause then there is a "fight" between what that voltage at the "short" is
suppose to be. Both sources will be trying to set it at there own voltage
and neither can win(well, practically one probably one or both will loose).

 

[JeffM]

[...]pick up Cool Edit pro 2.0

The payware product hasn't been called that for several years.

Adobe bought out Syntrillium and renamed it Audition
Right.

[...]go on eBay[...]

No need for that.
http://www.google.com/search?q=Cool-Edit+oldversion

and do all the mixing in the PC.

I thought you had veered of into a ditch--but nope
http://www.google.com/search?q=Cool-Edit+real-time
( It also depends on the application.)

I was thinking *open source*:
http://www.google.com/search?q=site:audacity.sourceforge.net+real-time-playback&filter=0
..
..
Jon Slaughter's *summing amplifier* link seems most apt
in the context of "synthesizer".

 

[[email protected]]

[...]pick up Cool Edit pro 2.0

The payware product hasn't been called that for several years.

Adobe bought out Syntrillium and renamed it Audition
Right.

[...]go on eBay[...]

No need for that.http://www.google.com/search?q=Cool-Edit+oldversion

and do all the mixing in the PC.

I thought you had veered of into a ditch--but nopehttp://www.google.com/search?q=Cool-Edit+real-time
( It also depends on the application.)

I was thinking *open source*:http://www.google.com/search?q=site:audacity.sourceforge.net+real-tim...
.
.
Jon Slaughter's *summing amplifier* link seems most apt
in the context of "synthesizer".

Last time I tried finding the freebie version of CoolEdit, there were
lots of references but all of them were dead ends. I checked on eBay
and it seems you can get a 2.0 for maybe $50 which is still an
excellent value for all it does. I've bought CoolEdit 96, 2000, pro
2.0, Audition 1.0 and 1.5 and use ver 1.5 frequently.

GG

 

[panfilero]

The word 'mixing' means 'arithmetic addition' to audio guys and
'multiplication' to rf engineers. When you multiply two sine waves,
you get the sum and difference of the two waves (carrier freq and
modulation in rf language). If one of them has harmonics like a
sawtooth, the product is the sum and difference of all the harmonics
in each wave. Real complicated and usually sounds like dogbreath.
Unfortunate overloading of an otherwise perfectly descriptive term.

Why is combining signals different for audio guys and rf guys? Isn't
there only one way to add (or mix) two signals? Which is that old
trig formula where you add and subtract stuff.... I don't remember
it....