Phase and Counterphase

There are two identical sine waves; if they travel in parallel, it is said that they are IN phase, but if one starts halfway relative to the other, they are in OPPOSITE phase

then theoretically they cancel each other out

Thanks, so a sound is in Phase when two sine waves travel in parallel.

But why does phase exist? and what happens when a sound is in phase? and when it is out of phase?

http://www.mineman.org/fisica/acustica/musica.php

thanks!! very interesting

i understood that the phase occurs when two (or more) sinusoids travel in parallel and therefore their positive peaks coincide, as do their negative peaks,

whereas in out-of-phase, the positive peaks of one coincide with the negative peaks of the other.

so when two or more waves are out of phase, what sounds do they emit? and why are waves sometimes out of phase?

thanks a lot

The phase of the sounds depends on the position of the sources. Normally in acoustics, one tries to calculate the correct positions so that the sounds are always in phase with each other (reinforcing each other). There are also cases where one seeks out the out-of-phase condition. For example, regarding large events, the position of the subwoofers is calculated so that a phase cancellation occurs towards the stage, preventing the sound from entering the stage microphones. This configuration is called cardioid sub.

beautiful!!! I didn't know these things, I don't understand acoustics and I have never done live recordings but I would like to ask this: I have software for editing audio (logic x) I don't know it very well but I am learning to record midi tracks using the instruments that the program provides.

Maybe the question is stupid, but there can't be phase problems between midi tracks right? or am I wrong?

I just read, while browsing the web, that there are ways to understand if, by analyzing a signal, it is in phase, or if it has out-of-phase or anti-phase elements that therefore deteriorate the quality.

Do you know how it's done?

I am asking this because sometimes I have happened to record several tracks; for example violins, violas, cellos, clarinets, horns, trombones etc.

and I noticed that there was something that didn't sound good at a frequency level, I believe, but this only happened if I played the tracks together; if instead I listened to them individually they sounded fine.. I don't know why this was happening..

can you help me understand? I discovered that I like acoustics, even though I am just a classical music student

Regarding the problem you are describing, try re-reading the part about beats.

For acoustics, get yourself a good textbook. There is also a lot online.

Open an ad hoc topic and then I will try to send you some references.

Fox wrote:

beautiful!!! I didn't know these things, I don't understand acoustics and I have never done live recordings, but I would like to ask this: I have audio editing software (Logic X); I don't know it very well, but I am learning to record MIDI tracks using the instruments provided by the program.

Maybe the question is stupid, but there can't be phase problems between MIDI tracks, right? Or am I wrong?

Phase problems between MIDI tracks are difficult unless they have been quantized. In any case, you always have to look at spatialization, as this is what causes the greatest phase problems. Regarding the mixing of live-captured stems, this problem always arises; at the time of positioning the instruments during the mixing stage, the phase correlation tends towards negative values. This is how Decca invented a system to remedy this problem by placing two microphones very close together with capsules 30 to 45° above the conductor's head to restore some centrality to the signal and remove these phase problems. In MIDI, we don't have this opportunity, but there are other mechanisms to keep the signal phase under control.

Fox wrote:

I just read, while browsing the web, that there are ways to understand if, by analyzing a signal, it is in phase, or if it has out-of-phase or anti-phase elements that therefore deteriorate the quality.

Do you know how it's done?

I am asking this because sometimes I have happened to record several tracks; for example, violins, violas, cellos, clarinets, horns, trombones, etc.

and I noticed that there was something that didn't sound good at a frequency level, I believe, but this only happened if I played the tracks together; if instead I listened to them individually, they sounded fine... I don't know why this happened...

can you help me understand? I discovered that I like acoustics, even though I am just a classical music student

Yes, as I mentioned before, there is a plugin called "Phase Correlator." If the indicator tends toward +1, it means the signals are in phase; at 0, the signals are 90° out of phase; at -1, they are 180° out of phase and there is cancellation. Generally, one always tries not to let the phase correlator go into negative values.

Regarding the frequencies, perhaps you are referring to equalization factors; to understand potential phase problems by ear, without a reference, you must already be quite experienced and have a very fine ear.

TheSimon wrote:

Phase problems between MIDI tracks are difficult unless they have been quantized. In any case, one must always consider spatialization, as this is what causes the greatest phase problems. Regarding the mixes of live-captured stems, this problem always arises; at the time of positioning instruments during the mixing stage, phase correlation tends to move toward negative values. Thus, Decca invented a system to remedy this problem by placing two microphones very close together with capsules at 30 to 45° above the conductor's head to restore some centrality to the signal and remove these phase problems. In MIDI, we do not have this opportunity, but there are other mechanisms to keep the signal phase under control.

Yes, as I anticipated before, there is a plugin called "Phase Correlator." If the indicator tends toward +1, it means the signals are in phase; at 0, the signals are 90° out of phase; at -1, they are 180° out of phase and there is cancellation. Generally, one always tries not to let the phase correlator go into negative values.

Regarding frequencies, perhaps you are referring to equalization factors; to understand potential phase problems by ear, without a reference, you must already be quite experienced and have a very fine ear.

wow! there is so much to learn and know, now I will look into the "Phase Correlator" plugin that you mentioned because I believe it is indispensable! thank you so much

If you use Logic X it is already included in the suite...

Videoclip wrote:

Regarding the problem you are describing, try re-reading the section on beats.

For acoustics, get yourself a good textbook. There is also a lot online.

Open an ad hoc topic and then I will try to send you some references.

Videoclip wrote:

Regarding the problem you are describing, try re-reading the section on beats.

For acoustics, get yourself a good textbook. There is also a lot online.

Open an ad hoc topic and then I will try to send you some references.

Thank you, I will re-read the piece about Beats more carefully and I will look for free handouts on the web, to start understanding the principles that govern acoustics

TheSimon wrote:

If you use Logic X it is already included in the suite...

Great!!! I'll look into it right away!!!

Sorry, I was reading the handout you suggested to me and regarding beating it says this: When two waves of slightly different frequencies interact, there are alternating moments when the waves are in phase (and therefore the amplitudes add up) and moments when the waves are out of phase (and therefore the amplitudes subtract).
The perceived frequency is only one, but the amplitude oscillates between a maximum value (the sum of the amplitudes) and a minimum value (their difference). This phenomenon is called beating.

In my own words, I think I understood that beating occurs when two sounds of similar frequency, by emitting different oscillations due to the different amplitude, produce an effect that is not properly distinct from the sound... for example, there can be beating between C and C + 0.1 Hz - did I understand correctly? I'm not sure.

if I have written in the wrong place, I will open a more specific post.

thanks everyone

Some insights on beats

http://www.pianoconcerto.it/forum/index.php?/topic/2261-lintervallo-piu-piccolo/

www.pianoconcerto.it/forum/index.php?/topic/508-battimenti-quinte

In this video at minute 44:30 I talk about beats...

Open content (youtube)

TheSimon wrote:

In this video at minute 44:30 I talk about beats...

Thank you so much, very useful and clear!!

Open content (youtube)

Kappa wrote:

Some ideas on beats

http://www.pianoconcerto.it/forum/index.php?/topic/2261-lintervallo-piu-piccolo/

www.pianoconcerto.it/forum/index.php?/topic/508-battimenti-quinte

Thanks Kappa!