Adding tones together...

[junglist_matty]

Hi,

I'm looking at the effects of adding tones together to try and improve my background knowlege about tones etc...

I'm using Audacity for this; all generated waveforms have the same phase.

- Channel 1: Generated a fixed frequency SINE tone at 100Hz
- Channel 2: Generated a fixed frequency SINE tone at 100Hz
- Channel 3: Generated a fixed frequency SINE tone at 100Hz

If I play channel 1 on its own I get a nice clean tone as expected
If I add channel 2 and/or 3 to play simultaneously with channel 1 it sounds like some sort of shift has happened,

What is actually happening? Does anyone have a weblink to an explanation?

Thanks,

[Rabalder]

http://www.earlevel.com/Digital%20Audio/Phase.html

[UKRuss]

It's simple physics really, wave interruption.

If the peak and trough of two identical waves occur at the same time as each other you will get silence. This would be known as 180degrees out of phase.

In order to avoid this you would need the oscillators to start generating their waves at exactly the same time. Most music related devices that produce waves can be set to retrigger, so you know that on each trigger of the notes you get perfectly in phase waveforms.

You will notice that the amplitude increases 100% for each additional wave you pop on top of each other, i.e. it will get louder.

When the waves are slightly out of phase as yours inevitably are, then you get the classic phasing effect that makes some bits louder and some bits queiter as the waves perdiodically enforce or destroy each other. once you get to more than two waves you make it very complex and this willr esult in a random sounding phase effect as all three waves start to collide and create a wierd phasing pattern.

[theophilus]

Hi,

I'm looking at the effects of adding tones together to try and improve my background knowlege about tones etc...

I'm using Audacity for this; all generated waveforms have the same phase.

- Channel 1: Generated a fixed frequency SINE tone at 100Hz
- Channel 2: Generated a fixed frequency SINE tone at 100Hz
- Channel 3: Generated a fixed frequency SINE tone at 100Hz

If I play channel 1 on its own I get a nice clean tone as expected
If I add channel 2 and/or 3 to play simultaneously with channel 1 it sounds like some sort of shift has happened,

Need more information on the bolded parts. From what you are saying, the 3 waveforms should be identical, no phase shifts or anything;
adding them together should only increase the volume. However, you could be clipping if you ran out of headroom; that would not sound like a sinewave anymore.

You're not manually looping these are you? It has to be exact as well. 100Hz at 44.100 Hz = 441 samples/loop, which should be exactly loopable, so shouldn't be a problem.

The alternative is that the mixing algorithm is not sample-accurate and is shifting the second/third channels relative to channel 1. This shouldn't give phasing - since the frequencies are exactly identical, the waveform in every period will not change, but it won't look like a sinewave anymore either.

[Tone Deft]

he's probably just clipping. constant phase differences can only cause volume changes, it would not introduce new frequencies. the only result should be louder, the same volume or quieter.

http://paws.kettering.edu/~drussell/Dem ... ition.html

lots of useful animated gifs on how waves add up.

[Tone Deft]

When the waves are slightly out of phase as yours inevitably are, then you get the classic phasing effect that makes some bits louder and some bits queiter as the waves perdiodically enforce or destroy each other.

that will not happen in this case, the signals are at the same frequency. you're talking about a beat frequency when sine waves are at different frequencies. this results in a beat frequency that modulates its amplitude at the rate at which the sine waves vary.

once you get to more than two waves you make it very complex and this willr esult in a random sounding phase effect as all three waves start to collide and create a wierd phasing pattern.

nope. it's simple, with more waves added the output will just get louder or softer, there will not be beat frequencies.

[junglist_matty]

Thanks guys, it was clipping... I set both tones to have an amplitude to 0.7 - thinking that would be low enough with having two tones added together that they wouldn't clip in the output; unfortunatley Audacity doesn't provide a volume level monitor on playback. I just set the amplitude to 0.1 and the tone sounds perfect,

cheers for the help, Matt.