When you sum a stereo source into a mono amp it causes some out of phase problems. If only there was some way to have the left channel go to the lower pole and the right channel to the upper pole...

For example: My Yamaha P120 and P90 digital pianos have only stereo piano samples, there are no mono piano samples in the keyboard.
When play theor stereo pianos through any mono amp the tone becomes thin, edgy and almost all attack. Other keyboards' stereo patches behave in a similar manner. When the left and right samples are summed on top of each other into mono there is a out of alignment problem that causes a chorusing and phase cancelation effect.
It's not the equipments fault, it's just what you get when you sum a stereo signla into a mono amp.

You may think, but most keyboards have a L/R mono output. Yes, but it sounds crappy because it is also suffering from out of phase problems.

Is there any merit a possilbe(future workaround) that would allow a stereo keyboard patch to be sent to the (top and bottom) of the tower. Just a question.

Phase, part 1
http://www.music.columbia.edu/cmc/courses/g6630/Phase.html.

Phase is a time relationship between two sounds, waveforms, or signals in a circuit. When the time relationship is coincident, the two signals or sounds are "in phase." And their amplitudes are additive. When the time relationship is not coincident, they are "out of phase" and their amplitudes are subtractive. This has ramifications both acoustically and electronically.

Example - Close miking a piano with two microphones. When you strike a key, the sound from the string will reach the closer mic sooner then the mic that is farther away, creating a slight timing or phase difference in the microphone signals. If those two signals are played on a stereo system the effect should be a stereo "image" of some sort. Our ears capture the same kind of timing and phase differences and the brain uses these differences for sound localization.

Now if the two signals from the two piano microphones are summed to mono, the phase difference between them could result in phase cancellation. In that case, certain frequencies, depending on the music content and the microphone distances, are reduced in volume as a result of the subtractive amplitude of the out of phase signals. (Conversely, if frequencies are in phase, the volume will increase.) The result could be a change in timbre of the piano, a decrease in volume of certain notes, or even a kind of distorted, dirty sound.

Whenever you are miking in stereo, especially close miking, it's a good idea to listen, then sum the two channels to mono and listen again. Then reverse the phase of one channel and listen again. This should tell you what frequencies are being canceled when you sum to mono. If you don't like what you hear, reconsider your microphone placement - phase is working against you.

ProTools has a Reverse Phase effect in the audio suite.

Sound reflections in a room can create similar cancellation effects, which recording engineers must consider in the room setup for a recording session.

petros,or bose. If this is a phasing problem (which it appears to be) would it make matters worse, or be worth experimenting with changing the polarity of the cord coming from one channel of the piano or the other? could it possibly correct anything? or would it just be a waste of time experimenting.

I was wondering the same thing. It would be easy to reverse the wires at one end of one cable.

so i was thinkin petros....i think i'll try it and just try the cable in the left, in the right,,along with the other cable wired correctly to the other piano jack...heck not much work and it will either sound better or it wont....certainly no elbow grease involved...

i tried it with an emu module i have here.....it really made a difference here....i have been having trouble with the middle register of the piano sounding somewhat hollow and dinky if you know what i mean. switchin the polarity of one of the cords coming from the piano, and then running them both into a stereo mixer channel and then to bose...quite a substantial difference...i like the tone much better..let me know what you think. i dont have my yamaha here now as i was going to sell it maybe...but i will get it back over wekend, and see how it reacts. im sure it will make a vast improvement also. but wont know till i try.
glad i read your post, as i wasnt able to put my finger on how to descirbe the tone I had completely forgot about phasing issues. And that is to me exactly about as near a description as i could have thought of.
im going to try this cord and scenario also with my computer pianos which seem to suffer the same syndrome and see if i like better.
if you try it, let me know if you could hear the difference. it does seem to warm up that middle register for me. at least with the emu.

Thanks wsf,

I'm curious to know what you get.

petros

Little Labs (http://www.littlelabs.com/ibp.html) makes a great phase alignment box called IBP (and a simpler junior version} allowing one of the stereo channels run through it to be continuously phase adjusted until it sounds right with respect to the other channel.
So there is an option instead of trying to force everything back to mono...

well at least on this emu module , it makes a huge difference. I do notice maybe a little less in the bass register, but its too me almost a good thing which can be compensated with eq.in th middle range of the keynoard i now can really hear the attack, and the string resonance, which i couldnt before. I am much happier now...been playuin all day through the bose like this, and i think its a great sound. much much more like a piano should sound i think.

sounds like an interesting little box h floyd..but i see its not cheap...but nice to know there is a tool out there like that.

quote:

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Originally posted by wfs:
well at least on this emu module , it makes a huge difference. I do notice maybe a little less in the bass register, but its too me almost a good thing which can be compensated with eq.in th middle range of the keynoard i now can really hear the attack, and the string resonance, which i couldnt before. I am much happier now...been playuin all day through the bose like this, and i think its a great sound. much much more like a piano should sound i think.

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Hi wfs,

I'm sorry, I don't exactly follow you.
What element are you referring to that makes a huge difference?

Thanks

I'm assuming you are talking about using a mono speaker setup for playing. I guess that makes sense in the context of a band and a single musicians amp. I wonder what other pianists do in this situation? Maybe Yamaha isn't the best gig keyboard for this reason alone. You don't see a lot of them in live bands.

Anyway, the Yamaha outputs are unbalanced. That means they have a signal and a ground. If they were balanced, they would have a positive signal, a negative signal and a ground. In that case you can play with reversing the signals. In the unbalanced case, I'm not sure you would get any sound at all. You would be feeding ground into your signal and your signal into ground. There must be some external component that takes a stereo input and allows you to mix them into a mono signal with the ability to adjust the individual channels phase delay and time delay and such when mixed.

ill try and explain petros but it may take a few lines , or a couple of posts
basically in the beginning i found my yamaha p80 to be very pleasing to me when i ran it through my own home stereo. very enjoyable to listen to and play.using both the left and right outputs of the keyboard into my stereo and having the left and right signals go to the respective left and right speakers. a wonderful sound.
when i bought the bose system. which was mono. the only way i knew to hook up was either run the left and right outputs of the yanaha into the ch1 and ch2 or ch3 and ch4 of the bose. basically summing the individual keyboard outs to the bose and setting the volume on the bose channels the same.
the first difference in the sound i noticed when going through the bose, was i had lost the stereo spread. the sound was very direct coming from one speaker column and not my stereo monitors.
then as far as tone. the bass register of the piano seemed ok, as did the high register of the keyboard. but the middle range of the keyboard seemd very hollow and unpronounced. especially when comparing it to the stereo sound i was used to.
i would try all kinds of eq, basically found i was lookin for somethin in the high mids to control. i tried every bose preset. tried cutting, boosting etc....but just couldnt hone in on a good sound.
ithen tried coming out of the yamaha, and going into a stereo mackie mixer channel. i liked the high eq control better. then id use an aux send from the mackie to one channel in the bose. it helped, but the middle range of the keyboard still sounded hollow, and just some odd artifact that just didnt sound as if the keys wee attacking the note right.
then i read your phase post and got the idea to try reversing just the leads on one end of a 1/4 in unbalanced instrument cord to see what would happen
you are correct. in doing this i essentialy have the ground wire in the 1/4 in going to the positive tip, and the positive wire is connected to the ground. I expected to hear quite a bit of noise if it even did work
but no noise, and there is a signal. im not sure why it is working.
but the difference i hear is that there is no hollowness at all now in my middle keyboard register. and the attck and the string resonance sound that was barely heard before is now much cleaner and the whole sound is a lot warmer. floyd above has recomended a product that im sure does whatever ive done or in a better way more eficiently and more electronically correct. of course if bose tells me that this may harm my system, well i wont be able to do it. but right now i am tickled pink in the difference and more warmth of my piano sound.
again basically my setup now is on my emu sound module is
one reg 1/4 in cord from the right output from the sound module. one cord where i reversed the one end and put the positive wire to ground, and the negative wire to the positive tip of the 1/4 in cord from the other sound module out. from the sound module i run these 2 wires into a mackie stereo channel. I then send the signal from that mackie channel to the bose using one of the mackie sends. I dont have my yamaha keyboard at the moment, but thats the way id hook up the yamaha to try it
i had a friend stop by and listen to the comparison to make sure it just wasnt somethin else that i thought i was hearing, and actually wasnt there. but he immediatly with no knowledge of what i did or was doing , also immediatly said he enjoyed the sound with the one channels reversed wire much better. hope that explains at least sorta what i did and why and what i noticed in the sound improvemnet.

agian, i think my biggest concern with this modification to the one wire is that the actual signal is now very suscepteble to noise. here in my apt there is no problem. but in the real world if this reversed cord i have made was next to anything that may cause interference like a power cord, some strange bar flouresent etc....it may not work with out catching alot of interference noise...basically i guess it really becomes like an unshielded cable. someone here may be able to tell you why i am hearing the difference that i describe in tech terms. but im just not sure. i am just going by my ears and what i hear. it just sounds better. probably the best you could do would just get an old cord and do what i did and see if you hear a difference. i would like to get the same results another way. but im not sure it would be very cheap. and would at least involve buying somethin a bit more complicated as the above mentioned by floyd.

also petros when i speak of the keybords middle register, im basically talking about middle c up and down an octave. tah particular range. hope all this explained it better? the emu sound module im using at the moment for this experiment is also unbalanced outs stereo left and right.

one last post...i still have yet to experiment with the actual yamaha keyboard, but wont get it back till sunday. however this morning i did try the technique with my computer piano samples.
coming out of my audio interface left and right i did the same type of comparison. but i really didnt hear much if any difference.

Wow wfs,

That is intersting. I am dying to find out what you think whem you try it with your P80. I may be able to try it with a P90 or P120 in the next week or so.

rtc

i'll let you know as soon as i have the oppurtunity to try it. I did find it strange that i noticed very little differnce in mny computer stereo samples. so i am guesing a lot is dependant on how the stereo samples were actually recorded in the first place ( mic placement, types of mics etc.) but i think its worth experimenting with. just as sometimes when playing my accoustic guitar. sometimes i would be in envirnments where bass was a real problem ( too much)....on occasion i would reverse the speaker wire polarity, and it would help significantly on my old system.
so it may be a hit or miss type deal. But like i said i couldnt figure it would hurt to try. it will either sound better or it wont, or maybe not make much difference at all. But i certainly wasnt pleased with the sound i ws getting so what did i have to lose. but now a total of 3 people have definetly heard the difference in my emu module. and all love the sound of the hookup with the reversed wire from one channel. i'll keep you informed.

"Interesting post.

What's happening is that you're reversing the signal (phase) of one of the channels. Suddenly the signals that were out of phase (and therefore cancelling each other out in the middle octave) are now in phase and the signal strengh is increased instead of being weakened which would boost the middle octave.

I would have thought though that the opposite would also apply, ie waveforms that were previously in phase would now be out of phase (presumably the octaves that sounded ok before swapping the wires). In fact I would expect the middle octave to sound unnaturally loud and the other octaves to fade away.... "

fancyfingers