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 Forum index » How-tos » Surround and Sound Reinforcement
Some thoughts about stereo
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PostPosted: Thu Mar 30, 2006 3:31 pm    Post subject: Some thoughts about stereo Reply with quote  Mark this post and the followings unread

Before we can get involved in surround systems, it's a good idea to think about stereo. This format is something we take for granted. Since it is so pervasive, we think we know everything about it, but there are certain problems with stereo that have been known since its inception in the 1930s that have been more-or-less ignored since it is so much better than mono.

To me, the most serious problems with stereo are:

1) the hole in the middle
2) the narrow center-line sweet spot
3) the sound field can not be wider than the speaker placement.

The hole in the middle

The hole in the middle problem comes about because even when a signal is panned equally between the left and right channels, the ear/mind perceives the sound as coming from the speakers. There is an illusion that the sound is in the middle, but this illusion is rather poor because the sound it perceivably coming from the left and right.

The movie people discovered this years ago and put in a third center channel for most of the dialog. To me, one of the most significant advantages of 5.1 over stereo is the center channel.

The sweet center line

Stereo is best when the listener is equidistant between the speakers. When the listener is off line, even by a little, the sound snaps to the location of the nearest speaker. For example, if you are sitting to the left, any sound mixed to both the left and right seem to be coming only from the left speaker. You hear sounds coming from the right speaker only when they are mixed to that side. Thus, the illusion of a stereo field only works when the listener is on the center line.

If you are writing music that uses stereo to create the illusion of stereo stage, then it will only be perceived if the listener is on the center line. In practical listening situations, this is relatively rare. It is unfortunate that when stereo is used in a concert environment, often there is a center aisle which eliminated the stereo effect for almost everyone in the hall.

The sound field is limited to the width of the speaker separation


This one may be obvious, but it contributes to stereo sound being very narrow. Some people do purposely generate out-of-phase components to trick the ear into hearing sounds that appear to come from beyond the speakers, but for the most part, all of the sounds are constrained to within the speakers.

Next time you go to an acoustic concert listen carefully. Even when the musicians are in front, the sound field is much wider than the visual appearance of the performers. This is because of the room acoustics. In fact, we hear sounds coming in from all directions.

When we listen to stereo, the sound is concentrated to within the approximately 40 degrees that separates the speakers. We don't usually object to this because we are so used to it, but IMHO it is a severe limitation and a factor that causes fatigue in the listener.

If one spaces out the speakers to increase the width of the sound stage, then the whole in the middle gets worse, so speaker placement is a double-edged sword.

---------------------------------------------------------------------------------

I have noticed that many commercial music releases are virtually mono. I think it is because of at least a tacit understanding of these problems with stereo.

For years I was never consciously aware of these problems, but in the last few years I've been working closely with Robin Miller. He's been developing some very sophisticated surround and 3D systems. I guess I'm starting to see the light.

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PostPosted: Fri Mar 31, 2006 3:33 am    Post subject: Re: Some thoughts about stereo Reply with quote  Mark this post and the followings unread

mosc wrote:
Before we can get involved in surround systems...


Thank heaven for posts like this!
I get so sick of reading posts from those who just don't get the whole surround idea that it is somehow not at all natural and as a result is something to be shunned.
Like Stereo is in any way realistic!

5.1 as we have it may well have it's drawbacks, but these are minor compared to stereo.

[editor's note: reduced the size of the quoted part of the message. --mosc]

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PostPosted: Fri Mar 31, 2006 6:36 am    Post subject: Reply with quote  Mark this post and the followings unread

welcome

Holy Canoli, Neil, thanks for joining our forum. From following the link on your sig, it certainly looks like you have quite a bit more experience than I have. I look forward to your contributions as this thing evolves.

I'm not "against" stereo, as I'm sure you are not either, it's just that I think it's good to be aware of it's strenghts and weaknesses. In fact, almost 100% of my music has been in stereo.

Last week I attened an excellent lecture/concert by John Eaton, one of the pioneers of live electronic music performance. I initially seated myself up front and to the left so I could be up close and see him. He started playing some prerecorded music he made in the 60s. To be frank, it sounded terrible. Most of the sounds came from the left speaker which was set up at the extereme end of the stage. The sounds from the right were weak and seemed out-of-place. I thought his music and technical skills were embarassingly bad.

Then I started to think about stereo and the things mentioned in my frist post on this topic. At the risk of being rude, I got up in the middle of one of his recordings and walked to the rear of the auditorium and took a seat on the center line. Voila - John Eaton's music suddenly sounded outstanding and his skills as a sound mixer/engineer are proved to be superb. What a difference! Even though I understood what was happening, I was astounded.

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PostPosted: Fri Mar 31, 2006 7:02 am    Post subject: Reply with quote  Mark this post and the followings unread

mosc wrote:
Then I started to think about stereo and the things mentioned in my frist post on this topic. At the risk of being rude, I got up in the middle of one of his recordings and walked to the rear of the auditorium and took a seat on the center line. Voila - John Eaton's music suddenly sounded outstanding and his skills as a sound mixer/engineer are proved to be superb. What a difference! Even though I understood what was happening, I was astounded.


This is remotely connected to what is called "colour management" and device profiling in the graphics industry. Intuitively colour is colour but yet that is not quite the case. In order to render colours correctly you will in fact need far more controllable factors than consumer systems have available.
So.. even if you get a nice book with pictures printed correctly you will in fact have to send a colour specialist team out to each and every one who bought the book and make sure that they have the correct lighting and whatnot. And ... digital imaging devices for consumers.. man.. there are issues.

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PostPosted: Fri Mar 31, 2006 7:24 am    Post subject: Reply with quote  Mark this post and the followings unread

It's one of the big misconceptions that Surround's sweet spot is seriously limited, and stereo is the better route.
If you are off-axis in a stereo situation, the sound is often ghastly - but in a 5.1 environment, you can hear the improvement in the soundfield even if you are completely outside the pentagram.
It simply fills the room up much better. Your live show analogy is well-known to me, as I used to be a FOH Live Sound engineer until injury forced me into my studio, and used to try & get around this by using infills - a mini stereo stack, just inside the main stacks, pointed at those in the front area who are well inside the cone produced by a stereo system. It helps, a little.

When there is a surround field, things sound much better across a wider range, and yes - it is true you don't get all the full benefits of the mix - but this is also very much mix dependant, as a lot of live shows released in surround merely have reverbs in the rears anyway.

This does not alter the fact that even with a 3.0 mix, things are a lot better anchored in the image with a true centre channel as opposed to the phantom centre produced in stereo.
The solution is simply to not use the same "head" - stereo is one way, surround is different. The problems start when surround mixes are essentially created as wide stereo.

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PostPosted: Fri Mar 31, 2006 7:58 am    Post subject: Reply with quote  Mark this post and the followings unread

neilwilkes wrote:

This does not alter the fact that even with a 3.0 mix, things are a lot better anchored in the image with a true centre channel as opposed to the phantom centre produced in stereo.

Yes, I have found this to be quite true. That center channel is a big improvement. I would like to start a separate topic about three channel systems.
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The solution is simply to not use the same "head" - stereo is one way, surround is different. The problems start when surround mixes are essentially created as wide stereo.

What do you mean "use the same head"?

To me a solution of these problems is to use a near mono mix when using a stereo playback system in a live situation. In other words, if there are people who are going to listening off the center line, then use mono or very shallow stereo.

Another solution is to put the stereo speakers very close to each other in the center of the stage so that from any audience member the angle between the speakers is not more than about 10 degrees. Unfortunately, the ususal case is very wide separation with the speakers at opposite ends of the stage - or the room.

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PostPosted: Fri Mar 31, 2006 9:16 am    Post subject: Reply with quote  Mark this post and the followings unread

Sorry about my dodgy terminology.
Embarassed
What I mean by "Use the same head" is that mixes in surround need to be approached in surround, and not in "stereo" mode. Have a really good listen to a lot of 5.1 mixes, and you will discover that the mix engineer was thinking in stereo - all too often I hear a disc where the majority of the audio is in L,R with limited material in centre channel, and just reverb in the rears. This is what I mean by "the wrong head", as the mix engineer was still thinking in stereo.
A great example of this has to be the well-known Led Zeppelin live set - extract some of the music in 5.1 and take a good look at the recovered waveforms, you will see it's basically stereo. All that is in the centre channel is a bit of page's guitar solos, the odd vocal delay, and that's about it. And all that exists in the rears is audience.
The mix engineer used his stereo head, not a surround one.

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PostPosted: Fri Mar 31, 2006 11:00 am    Post subject: Reply with quote  Mark this post and the followings unread

stereo is ok if you want people's eyes to bounce back and forth, following the sound from one random speaker point to another...ooohh that hi hat came from the 'left hand side'...perhaps it's best when it is a 'sound stage' and stereo panning represents physical positions of player's on a stage...but it usually sounds as phoney as a 2-dollar bill

stereo is often used to hide bad mixing

always check a mix in mono...make sure it's all sounding good in mono...then, do a bit of panning if you want for SPECIAL EFFECTS ..like in the movies heheh

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PostPosted: Fri Mar 31, 2006 11:28 am    Post subject: Reply with quote  Mark this post and the followings unread

Well, technically we are using the stereo file for delivery of mono too, which of course does not compute. Ideally a mono mix is s mono mix and shouldn´t simply be the sum of L + R .

But yes, the original Abba mixes do sound awful both in mono and stereo. Laughing

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PostPosted: Fri Mar 31, 2006 3:41 pm    Post subject: Reply with quote  Mark this post and the followings unread

No.

None of Mosc's points affect stereo to any signifficant degree; this is about mono panned between two speakers, that's something completely different from real stereo.

If you have holes in the middle, if your stereo image is limited to the space between the speakers, if the speakers draw atention as "points" then you should learn more about psychoacoustics and apply it to your mixes. It's not about that "pan" knob, "pan" is like using presets. It's all in the eq, the use of delay, phase and only a very small bit is in the volume. It's trivial to make a sound louder in the left chanel and still make it sound like it's coming from the right direction.

If you can't do that or if you can't hear the difference then yeah, n.1 will probably make sense to you and will apear like a improvement. That has nothing on stereo in the hands of a expert. It's the same as the discussion on the axis of 3d sound; stereo does have two axis; you can easily define distance but you need to realise how distance works; how it affects sound. Most importantly; it doesn't matter all that much what the sound actually is; what matters is how it's preceived, you should mix to the hearing psychology, not to the speakers, not even to the ears.

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PostPosted: Fri Mar 31, 2006 4:09 pm    Post subject: Reply with quote  Mark this post and the followings unread

paul e. wrote:

always check a mix in mono...make sure it's all sounding good in mono...then, do a bit of panning if you want for SPECIAL EFFECTS ..like in the movies heheh


I agree there, particularly is there is any chance of it being played in clubs.

I don't nesicarily agree with it but many large venues use mono systems.

Mono does not need to mean a lack of depth; with some clever trickery and good listening you can create a evocative soundstage on a single speaker. You always have "distance" left. Distance works on your hearing in a profound way; a lion at 50 meters means "plan" regardless of the direction, a rattlesnake at your feet means "jump f*ing NOW, think later!"

Anything that moves in the "distance" dimention will draw the atention of the hearing. "Should i chase the girl?", "should I relax about the panther?" are the sort of question that the part of your brain that interperts these things before you wonder what the neigbour will think of your speakers cares about.

This is the last I'll say about it because it's a endless discussion but your audience that you are mixing for is a hunter-gatherer that can use a small vocabulary, can manipulate symbols at a rudimentary level and that cares about eating, being backstabed, reproduction and if you are lucky the coming winter. this affects 1, 2, 6 or 900 speakers equally.

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PostPosted: Fri Mar 31, 2006 8:09 pm    Post subject: Reply with quote  Mark this post and the followings unread

Kassen wrote:
you should mix to the hearing psychology, not to the speakers, not even to the ears.



nice........good posts

perhaps mixing to all three aspects [psych./ears/speakers] in some order of priority ?

question for someone...do we really hear binaurally just because we have two ears

or do the two ears essentially sum the left and right to a mono channel..and then some other brain mechanism interprets 'distance' and azimuth etc??

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PostPosted: Sat Apr 01, 2006 1:15 pm    Post subject: Reply with quote  Mark this post and the followings unread

Paul. There are many mechanisms used by the ear/brain to figure out direction, distance and motion of sounds. People who have only one ear can still perceive these to some degree. The head and the pinna cause certain phase shifts and frequency attenuations which we have learned to interpret on a subconsious level.

Kassen. No matter how well mixed and artful one prepares their masters, the ear/brain of the audience when listening to conventional stereo will eventually figure out it's not listening to a continuous sound field that extends across the apparent stage, but to two speakers. This is especially the case if the listener is allowed to move their head while listening. It is very easy to hear that the stereo image is only as wide as the speakers. Once your ear/brain gets that it starts hearing the hole in the middle, even if the left and right speakers are playing the same signal. If you are even slightly off the center axis, this perception is all that much faster.

We have listened to stereo so much we tend to overlook this limitation in the system. I'm not saying stereo is bad on an absolute sense, but it does have this limitation, at least to many observers.

There is a stereo system that gets beyond this - it's call Ambiophonics. http://www.ambiophonics.org/ One of our members here, Robin Miller is a recognized expert in this system. It uses DSP based phase cancellation algorithms. The two speakers are placed very close together in front of the listener - separation is about 10 degrees. It is amazing how this system produces localization that is very wide - 160 degrees. If you have never heard an ambiophonic demo, try to do so. It's quite dramatic. Ambiophonic has it's own problems, especially the very small sweet spot, but for the "front sound stage" it is superb.

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