Audio Mixing Question...

Discussion in 'The Projects Forum' started by Artfldgr, Oct 17, 2010.

  1. Artfldgr

    Thread Starter Active Member

    Aug 15, 2008
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    1
    Hey all,

    here is the point of my problem...

    I dont hear in one ear, and so everything has to be in mono if i want to use a ear bud. however, stereo to mono plugs and other tiny adaptors really suck.

    the point is that mixing electronic signals is nothing like mixing the sound from two sources in a room. listen to certain pieces in a room, and i hear everything, listen to the two channels put together, and sometimes the mixing cancels each other out. so i get voice, almost no music, music no voice, background fading and being replaced by foreground...

    is there a way to mix two signals so that what happens stops happening?
    i was going to shift phase slightly.... that way nothing matches up exactly.

    any ideas or comments welcome..
     
  2. Audioguru

    New Member

    Dec 20, 2007
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    Most of us hear in stereo so if sounds are out of phase at each ear then they don't cancel like when mixed into mono.
    You must add a replacement ear to hear stereo normally. Sorry.
     
  3. marshallf3

    Well-Known Member

    Jul 26, 2010
    2,358
    201
    sometimes the mixing cancels each other out. so i get voice, almost no music, music no voice, background fading and being replaced by foreground...

    Yup, that's happening when the two sources are out of phase with each other and it will vary depending on frequency, room dimensions etc.

    What might help is some osrt of headphone that has two separate drivers in the same side.
     
  4. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    3,795
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    When ever we had an out of phase condition in the stereo field, we simply reversed the speaker connections of ONE speaker.

    Problem solved.
     
  5. Audioguru

    New Member

    Dec 20, 2007
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    Remember when stereos were sold in a stereo store? The salesmen always had the speakers connected out-of-phase and the bass was cranked up way to much to try to reduce the cancellation. I would quickly reach around and reverse the phase of one speaker so that both speakers were in-phase then turn down the bass to normal and then the sound was much better.

    One day a local FM station broadcasted some music with the channels out-of-phase. In mono some of the music was very faint. I called the engineer and he said that he knows but there was nothing he could do about it.
     
  6. wayneh

    Expert

    Sep 9, 2010
    12,156
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    That might work if you were listening to a single frequency, but of course you're not. So I'm not so sure a phase shift will cure the wave interference issue. Fix it at one frequency but perhaps make it worse at another. I wonder if the two-drivers-at-one-ear approach isn't a better idea. Mechanical problem.
     
  7. Artfldgr

    Thread Starter Active Member

    Aug 15, 2008
    44
    1
    that was a nasty answer...

    especially when i was a child and was turned down on getting a chochlea implant...

    no sh*t most hear in stereo
    and most people speed through yellow lights beeping and assuming everyone can hear...

    what you dont get (smart ass) is that in a room i can hear the music fine. no i dont get location information since i have one ear, but i hear it the same as you...

    without a second ear, i am missing only the sensation that a drum is to the left, and a guitar is to the right of me...

    however, as i explain in my post... when ELECTRONICALLY Mixing, the sound guys inverted the signal to the other channel in alignment... so what happens is mono adapters cancel

    now here is the nifty part... if you hear this mono version, and it was played to the room, you would hear what i hear, and bascially singing parts with no music, music with no singing, in and out audio..


    and yes i know the physics of why in a room it works, and why not when its an electrical signal.

    what i am trying to do is figure out how to add them up so i can hear them at my desk... and i dont want to make a small box with two speakers and one microphone... :p

    basically telling me to be reborn without the handicap is not a nice thing to say, imply, etc...
     
  8. Artfldgr

    Thread Starter Active Member

    Aug 15, 2008
    44
    1
    its a tough problem..
    and MOST of it is exhibited in the early mixes from the first studio recordings where they didnt actually play the way it was in its final form.

    however i am at a desk, and i ahve to listen with an ear bud..
    and i HATE that a lot of the songs that i like coming over online radio cant be heard since they mixed it this way.

    right now i am thinking of putting a pieve of foam in a small tube wth a small speaker at each end. slots cut to prevent it being seen by the pressure waves as a tube, and put a electret with a flat response in between them.

    as far as shifting the frequency, i was going to do that one, to one and a half the width of the lowest frequency...

    the idea is to pretend electronically that the two speakers (imaginary) are a distance apart, and so have a different time of reaching the ear as it does in a real room.

    if the whole is shifted farther than the lowest wavelength, then all the lower will be shifted as well..

    electronically, without a delay, the system sees both audio sources as if they are from the same point in space and time... and so exacly the same that an inverted channel can cancel the other...

    but if two sources were near each other, this would not happen...
    or rather would not happen as a perfect alignment, but would phase in and out along the various distances that are equal, and unequal...

    add to this bounce off of walls. and cancellation is not something that works except in part. [you wont see them make a speaker system that you can turn on in a room and cancels all sound]

    stereo to mono basically sums them at one point
    where two speakers sum them across a plane of points.

    with sufficient spread, as if there was more than one speaker two areas of a room
    it would sound great...

    too much spread, and you will have bypassed your brains delay..
    and you will start to hear it as an echo...

    [we developed this cancellation because we lived in enclosed spaces, like caves]

    delaying one channel relative to another, is not an easy thing...
    espeically when you are workign with analogue not digital..
    [you could do this easy in digital with a delay buffer for one channel before the decode]

    in analogue about the only thing i can think of doing is a chain of op amps.
    invert the signal twice, then match it with the other...

    so each op amp is a delay.... (and noise)

    putting 4 opamps as followers will delay that input signal compared to the other signal that is passed directly to the output of the 4th...

    oh... and i cant use a regular headset.
    you put that on me, and i am DEAF to thw world
    i wont hear fire alarms, people asking questions, etc...

    not good.

    also, if i come up with something nice, others with the same problem can copy the circuit... and not have to pray to god to give them stereo hearing next time they are born
     
  9. Audioguru

    New Member

    Dec 20, 2007
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    896
    A delay will work for only one frequency if you and the sound source do not move. The delay can be adjusted to add the two channels. But at different frequencies it subtracts and cancels. Adding a delay produces a comb filter that has many peaks and nulls almost like mixing stereo into mono. A delay will not do what you want.

    If the recording is done correctly then a singing single person is on one channel or the other channel or in between. Mixing the two channels into mono will sound fine.
     
  10. Artfldgr

    Thread Starter Active Member

    Aug 15, 2008
    44
    1
    I know if things are done right it will sound right, but back then they didnt mix like they do today... and some music today does it.

    cant get pandora to make special recordings for me, and my tardis is broken so i cant go back and talk to the studio guys who were just inventing stero...

    i can neither become undeaf in the deaf ear
    or go back in time to have the pros remix their work
     
  11. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    6,357
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    I just put in the right earbud and get by.

    To hear from the left ear, I'd have to crank it to the point where my right ear would go deaf too.
     
  12. Still Learning

    New Member

    Jul 19, 2010
    25
    0
    Hearing protection is paramount-I can't mix with 'tired ears' and any engineer will tell u that!

    Alot of engineers test their mixes down to a single speaker, auratone style to check how it will sound over radio (as alot still are played in mono/compressed to the sh!tter and sounds terrible unless adjusted first!), but when listening to online audio I would say this step has been neglected!

    Phase is the main issue you will face but by the sounds of your improvised techniques, you've already looked into this aspect quite a bit!
    I'm sure there has to be some form of software/plugin that will correct phase shift, but an on-the-fly system would not be accurate or great quality still, as already mentioned..

    Interesting issue, wish you the best and please let us know if you find anything that helps-could not only benefit youself but quite a few people!

    ..I really haven't been that much help, sorry!
     
  13. Artfldgr

    Thread Starter Active Member

    Aug 15, 2008
    44
    1
    been thinking on this one for a while...

    the EASIEST solution is to get a headset with a nice large ear piece, convert it to a one sided headset (why cover the other ear?), and then gut the whole thing running two ear buds glued to the inside... :D


    not really going to cut it i guess for those that want a better solution...

    by the way, this is mostly a problem in the recordings from the early days of mixing, and the days when audio didnt have extra information as to dolby...

    here is a potential solution i am thinking of playing with...

    PT2399

    PT2399 is an echo audio processor IC utilizing CMOS Technology which is equipped with ADC and DAC, high sampling frequency and an internal memory of 44K Digital processing is used to generate the delay time, it also features an internal VCO circuit in the system clock, thereby, making the frequency easily adjustable. PT2399 boast of very low distortion (THD<0.5%) and very low noise (No<-90dBV), thus producing high quality audio output. The pin assignments and application circuit are optimized for easy PCB layout and cost saving advantage.



    the idea here is to delay one signal to add "dimensionality" to the audio...

    that is, rather than play the music as if both sources are from the exact same point and so can cancel each other in ways that in a real room just cant happen.

    the imperfect illusion is what you would get if you had a speaker near you and another a few meters away.

    To implement such a delay from scratch would be ONEROUS...

    I havent really looked at detail, but as long as there is a class of chip, maybe one of them would be good. :cool:

    On the flip side i have a home office solution for myself :p

    i took apart an old set of Dell Speakers... and now am putting them both into one box. this will allow for four - six inputs. IE. i can combine the audio from several computers and a tv set up.

    its a nice little set up.. taking apart the wacky shaped speakers (4 Ohm), and reusing the amplifier board (6 watts), and adding a few things, like an input stage, and a switch to connect pins 8 and 7 (which will add mute!)

    i am debating whether to have the input all melt together, and just let the computers audio and all that do the settings...

    in this way i may be able to hook up 1 television, and 3 computers to all use one audio, and one power source...

    i have to do more reading but i may decide to use the
    PT2323

    PT2323 is a 6-Channel Audio Selector utilizing CMOS Technology specially designed for Home Theater System. It provides a built-in 2-Channel to 6-Channel Translator, which can directly mix traditional stereo channel to simulate a 6-Channel audio output. Single power supply (9V), I2C Bus Interface as well as very low Total Harmonic Distortion (THD < 0.005%) and other features are incorporated into a single chip thereby providing very high performance. Pin assignments and application circuit are optimized for easy PCB layout and cost saving advantages.


    both chips are pretty cheap... with postage and stuff not more than $2 each...

    its interesting that if i add a jack, i can then mix and put out a 6 channel signal...

    but in this case, i would probably just be using the 4 stereo channels, and the one output... it says it has an I2C bus interface, but the docs i have (so far) doesnt say what its for... or what signals do what...

    any ideas guys (and gals)? :)
     
  14. Markd77

    Senior Member

    Sep 7, 2009
    2,803
    594
    I'm not sure how this could be implemented but it's possible that adding a tiny amount of echo to both channels and then mixing might work - it would simulate the 2 speakers in a room situation.
    I'd agree that just delaying one channel probably won't work too well.
    It would probably be worth testing in some audio editing software first because I can't guarantee it would work.
     
  15. Audioguru

    New Member

    Dec 20, 2007
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    A small echo causes exactly the same cancellations as mixing stereo into mono.
    A room also causes the same cancellations because of reflections (from the floor, walls and ceiling) having a longer path causing a delay.
     
  16. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,754
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    If U want mono signal from a stereo one, then all u have to do is sum it.

    A summing amp will combine the stereo signal in to a mono one
     
  17. Audioguru

    New Member

    Dec 20, 2007
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    His concern is that some phase shifts cancel some frequencies when the two channels are mixed together. He does not want cancellation.

    Please type complete English words. U and u are not words. You is a word.
    Are you trying to type on a cell phone?? Please use a computer keyboard instead.
     
  18. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    why guru..do u have a hard time reading it..
    It's not sms texting. cell texting is worse.
    I use "u" , "abt" for ease of writing....

    chill dude....

    as for OP... Summing will not cancel anything. Mixing channel do not cancel out signals. If they do, people wouldn't be using Mixers in Studios and sound stages.
    This may be new to u, as for me I deal with this everyday

    I don't understand why you guys are taking OP's problem way out of line.
    What OP want is such a simple thing....and yet ...
     
  19. Artfldgr

    Thread Starter Active Member

    Aug 15, 2008
    44
    1
    A small echo causes exactly the same cancellations as mixing stereo into mono.

    no it doesnt...

    if two complicated varied waveforms cancel when i mix them in mono...
    they wont cancel when there is separation to them...


    A room also causes the same cancellations because of reflections (from the floor, walls and ceiling) having a longer path causing a delay.

    not the same... whats happening in a room is more akin to waves on the surface of a water constructively and destructively interfering with each other.

    this is why you cant flip a switch and make the room silent...

    but you CAN invert and apply a lower dimensional signal and it will cancel.


    this is the difference between mono in a headset, and mono in a room.

    go ahead, listen to some of the Beatles albums with a mono adapter, or Crosby stills Nash young...

    today i heard the latter, and in this case, the audio canceled out almost everything except three singers in one section!!!

    if i play it to the room, there isn't any problem it cant cancel out that way if your playing through two different speakers.

    if you look at the applications sheet for that chip, one application is echo

    the other is basically what gives you the hall sounding effect, and other effects of making your room sound bigger by playing with the delay in your home entertainment system.

    your brain also cancels out repeating noises (echos) when the delay is too small... (i think this is an adaptation to listening in caves, and shelters without hearing echo which is there but we dont hear it).
    Phase delay enhances 3D audio

    http://www.maxim-ic.com/app-notes/index.mvp/id/4632

    the article is about Trans-aural Crosstalk...


    since i am deaf in one ear the ONLY thing i am missing is distance information from hearing how the waves separate in time.

    this means that i cant do the 'cocktail effect', which is to filter audio by direction...

    everything else is in the audio (at one time i played solo clarinet despite being deaf on one side), its just not separable


    whats interesting is that this effort of theirs to play with the sound to make 3D breaks up the mixing so that in simple mono, there is no problem..

    the problem comes mostly (not always) the classic tracks from the early days of stereo, and even quad sound...

    When listening to sound from a two-speaker source, the left-channel signal arrives at the left ear before it arrives at the right ear, and the right-channel signal arrives at the right ear before it arrives at the left. The right ear, however, hears a little of the left-channel sound, and the left ear hears a little of the right-channel sound. That effect is called transaural acoustic crosstalk - from linked article

    so reproduced audio played to a room has qualities that head phones never have, and the difference to me because of the handicap is so noticeable.

    technically, they should have different HRTFs (head related transfer functions) depending on whether the audio was to come out of speakers, and whether it was to come out of headsets. [they probably do!]



    originally i was going to try to bring out the sound in these recordings by adding a delay so that they cant cancel each other perfectly as they do with mono resistor converters.

    [and the maxim article bears me out on the physics]

    the problem is that the circuits become big huge complicated things that really should be in a top of the line 3D audio experience.

    and all i really wanted was not to suddenly hear only the back up singers as the audio cancels using mono adapters (resistive). [its even worse when its like an early floyd album, where they really played with the back and forth... ack!]


    well i was looking at cheap chips i can buy to have fun with (doesnt everyone?), and thats when i noticed the [SIZE=-1]Echo Processor IC...

    its used for several things...
    and echo feeding back and fading itself is just one...
    pedals for guitars is another...
    Karaoke machines, and audio labs...


    if you heard some of the ways i was thinking of doing this...
    one was to mix in a pwm mix, another was a bizarre thing using two laser pointers :eek:

    but then i saw this chip... for under $2

    and on page 4 of the documentation (datasheet)

    PT2399 SURROUND/DELAY APPLICATION CIRCUIT

    that is, its used to make surround sound work...
    different delays correspond to pretending your speakers are farther apart than they are, and or the room is larger than it is... (or has more echo)

    rather than have to make a graphic equalizer in which each bands waveform is 90 degrees... i can use this chip

    now when i mix, its going to sound to my ear as if i recorded from a microphone in a room where the sound source is far apart, and not unity.

    [physics is my big thing... :cool:]

    ultimately this is a perfect solution...
    for a reasonable cost in parts, chip, and time..

    i can implement a small delay in one channel before i mono mix them...
    as long as they are within a certain separation, it will be like adding dimension




    the other chip was a bonus find as it would allow you to process up to 6 LR audio channels, and output a 6 speaker version... however... i can mix the channels... and rather than use the 6 channels, i can drop two of them, and mix the bass boost back in... have to read the datasheet more.. so right no consider this a pipe dream

    but the surround delay should be a good fix for us Aural challenged folk... ;)


    [/SIZE]
     
  20. Artfldgr

    Thread Starter Active Member

    Aug 15, 2008
    44
    1
    R!f@@
    I think your missing the point...

    the audio was mixed in a studio down from several tracks to just two

    in the early days of stereophonic sound, these mixes were odd compared to later.

    i am not the only one aware of this as they have re-issued many titles with mono tracks... and visa versa

    here is an example

    Bob Dylan's mono recordings, 1962-1967
    news.cnet.com/8301-13645_3-20018581-47.html


    "John Wesley Harding" was the last mono LP from Dylan; after that all subsequent American releases were stereo only. So unless you have original 1960s-era LPs, chances are you've never heard the mono mixes.

    The stereo versions of Dylan's music sound fine, but as Berkowitz put it, "Up until the Beatles released "Sgt. Pepper," mono was the real production format, and stereo was an idea to comply with." I'm usually a stereo guy, but I have to admit that the single CD advance copy of "The Best of The Original Mono Recordings" convinced me, at least for Dylan, of the mono mixes' superiority. The differences aren't subtle.


    and here comes the point i am trying to make...

    The first three albums, "Bob Dylan," "The Freewheelin' Bob Dylan," and "The Times They Are A-Changin'" stereo mixes are the worst "offenders" in that Dylan's vocal is centered, his guitar is all the way over on the right, and harmonica on the left.


    if thats all they did then it would be fine..

    but other studios on other albums did things like split the instruments between two channels with the worst being they inverted the signal, so when its in mono, the instruments disappear and all you have is a tambourine and a singer, with an off key backup (which would not sound off key with the music).

    Smile (The Beach Boys album)


    en.wikipedia.org/wiki/Smile_%28The_Beach_Boys_album%29


    Despite the availability of stereo recording, Wilson always made his final mixes in mono, as did rival producer Phil Spector. Wilson did so for several reasons -- he personally felt that mono mixing provided more sonic control over what the listener heard, minimizing the vagaries of speaker placement and sound system quality. It was also motivated by the knowledge that pop radio broadcast in mono, and most domestic and car radios and record players were monophonic. Another, more personal reason for Wilson's preference was deafness in his right ear.


    and Duophonic is a major source of this 'effect'
    and key for this post...


    so as you can see... my hearing issue when using headsets lets me know which recording that people with two ears often cant tell whats going on :cool:

    but to not listen to miles davies, the beatles, Crosby Stills Nash and Young, Beach Boys, and really very large amounts of music from those days...



    so this 'fix' may be a good one... :)
     
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