My old article on Loudspeaker Imaging

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Re: My old article on Loudspeaker Imaging

jeff, the meat to potatoe ratio was just fine. i read a post earlier by lunch and lunch said "So.... yes, this made a really big difference... the sound stage is much deeper and more spacious now, and yet the imaging is also tighter... Miles and Coltraine sounded incredible. Every musician had their own distinct position about 10 feet behind the speakers... close your eyes and smile " in this post

http://techtalk.parts-express.com/showthread.php?t=213695

your thoughts on this?


thanks for another great writeup if had gotten much more technical i probably would have not finished it.

[dbe]

Re: My old article on Loudspeaker Imaging

Bump

--It hasn't been that long since this thread was originally opened.
--It seems like higher resolution DACs should better be able to reproduce the micro dynamics.
--A good combination of directivity control, power response, low distortion drivers and low order crossovers ought to make for good imaging.
--Which frequencies are most critical to imaging>?

Yep, this is a great topic for discussion as it is one that has so many aspects that can be discussed an debated to the cows (or dogs or your favorite animal inserted here___________) come home.

Capturing an acoustic event in a good stereo recording is the product of proper micing techniques that are time tested (Blumlein, Decca tree, et al) or some new revisions on technique such as Ray Kimber's Iso-mike which gives breathtaking results.

Studio localization/isolation recording is a completely different animal which uses the different panning techniques discussed above (I think, it has been a long time since this thread was written). The different techniques in recordings yield different results on different speaker types. This was readily apparent as I walked around at RMAF. Too many etched, excessive HF systems for that audiophile "gotcha" sound. It is exciting to listen to for about 2 minutes: huge soundstage and larger than life instruments that give way to figeting and leemee oudahere thoughts in no time.

As always, what makes good imaging in a speaker is faithful recreation of a good recording with low distortion and coloration. The TAD speakers did it in aces.... for $60K. A few other rooms sounded good, too. The ones that did worked the room for all it was worth. Treatment where necessary and good music selection makes a world of difference.

I'm glad to see this topic live again. Maybe one of you guys will start a new one and get some discussion going. Me, I'm headed to bed.

Later,

Dave

[Deward Hastings]

Re: it's all illusion

Depending on the hall architecture and mic placement, different orchestral recordings can contain very different depth information.

Yep. And that architecture and placement information is rarely disclosed in album/liner notes, so it is difficult to draw any conclusions. The recordings with the most obvious "depth" may well be multi-miced (quasi studio recorded) and the "depth" cues entirely artificial. I've seen examples where an orchestra's album picture was an entirely different venue than that in which the recording was made (with no disclosure of that in the notes). Opera recordings in particular are commonly "studio" recorded, and the sound of the recording bears no resemblance to what you would hear at an actual performance (with the orchestra in the pit and singers on stage). Even the "thumps and bumps" of a stage performance may be faked in the studio or added in post, like Foley effects in a movie.

[brianpowers27]

Re: My old article on Loudspeaker Imaging

After thinking about this article I decided to take a mono recording of my acoustic guitar with the ecm8000. I took the same track and presented it three times, one raw, one with an artificial stereo and one with artificial stereo + reverb + multiband compression.

I think it is interesting from the standpoint of seeing what recording techniques can do to the sound. I would like to get a second mic and take stereo recording with me walking around the room.

http://techtalk.parts-express.com/showthread.php?t=213684

[brianp]

Re: it's all illusion

"Depth" perception is a bit different, and in orchestral recording I believe it comes largely from the delay time of rear wall or shell reflections. It's clearly not an amplitude effect . . . the trumpets can play loud or soft and not seem to move, but if actually moved on stage that is immediately obvious. For instruments downstage (usually strings and piano/other soloists) the shell reflection is substantially delayed (the round trip is, after all, a minimum of 50 and often as much as 100 ft.) or completely lost in other hall reflections. Instruments placed further upstage have an earlier reflection, which we interpret as them being closer to the shell, or further away than the strings. That may give a sense of "depth" even in a monaural recording, at least to someone familiar with live orchestral sound. Pronounced "front wall" reflections in the listening room can completely swamp these recorded clues and limit the depth illusion to no deeper than the speaker-wall distance, if that.

Depending on the hall architecture and mic placement, different orchestral recordings can contain very different depth information. I set up a little system out in the back yard for most of the summer, where there were no listening room reflections to confuse things. Some orchestral recordings had tremendous depth, while others seemed to put everything at the plane of the speakers.

[Deward Hastings]

it's all illusion

and as Dave (dbe) points out one can create localization illusion easily at the console . . . in fact "localization" in *all* studio recording is "fiction" to some significant extent.

Live recording a symphony while preserving lateral "localization" is a different story . . . it's often difficult to localize instruments, or even whole sections, from more than half way back in the hall *at the performance*. Of course the mics are placed closer than that, and there are both amplitude (spaced and Blumlein) and phase (ORTF) cues that *can* (but do not always) provide "better than life" localization (ORTF placement actually includes both amplitude and phase cues, as does the "Decca Tree", and those placements probably give the best localization results (unless sections/instruments are miced individually and false cues added at the console)). I believe that the "phase" cues really amount to little more than "relative time of arrival" . . . that being what our ears actually hear. It is obviously frequency dependent (which is why we can localize high frequencies better than low), and it all has to happen before first reflection from the listening room. After that we are hearing room size cues which may or may not let us ignore the immediate listening environment and "hear the original venue".

"Depth" perception is a bit different, and in orchestral recording I believe it comes largely from the delay time of rear wall or shell reflections. It's clearly not an amplitude effect . . . the trumpets can play loud or soft and not seem to move, but if actually moved on stage that is immediately obvious. For instruments downstage (usually strings and piano/other soloists) the shell reflection is substantially delayed (the round trip is, after all, a minimum of 50 and often as much as 100 ft.) or completely lost in other hall reflections. Instruments placed further upstage have an earlier reflection, which we interpret as them being closer to the shell, or further away than the strings. That may give a sense of "depth" even in a monaural recording, at least to someone familiar with live orchestral sound. Pronounced "front wall" reflections in the listening room can completely swamp these recorded clues and limit the depth illusion to no deeper than the speaker-wall distance, if that.

It is also amazing just how much a picture of the orchestra (actual or remembered (imagined)) can help in "localizing" the individual instruments . . . ;)

[brianpowers27]

Re: My old article on Loudspeaker Imaging

Read Blauert "Spatial Hearing"

Available online for free viewing

http://books.google.com/books?hl=en&lr=&id=wBiEKPhw7r0C&oi=fnd&pg=PA33&dq=%22Blauert%22+%22Spatial+hearing%22+&ots=4Hq91PaZ7e&sig=tQ9gO7blu-yQvY3lPJEtnxhtAv0#v=onepage&q=&f=false

[Paul Carmody]

Re: My old article on Loudspeaker Imaging

--Which frequencies are most critical to imaging>?

Read Blauert "Spatial Hearing"

[brianpowers27]

Re: My old article on Loudspeaker Imaging

Bump

--It hasn't been that long since this thread was originally opened.
--It seems like higher resolution DACs should better be able to reproduce the micro dynamics.
--A good combination of directivity control, power response, low distortion drivers and low order crossovers ought to make for good imaging.
--Which frequencies are most critical to imaging>?

[dlr]

Re: So much of what's been said...


> But there are some heavily-engineered discs
> out there that will employ certain tricks to
> generate illusions of sounds coming from
> farther beyond the speakers. Part of how
> they do this is by employing phase
> cancellations. Shoot a selected sound, say
> from the left speaker, and then shoot a
> phase-cancelling signal from the right, with
> appropriate sound muffling, to
> minimize/cancel what your right ear gets to
> hear. You can tell there are a lot of things
> that can go wrong so really not a lot of
> systems (in their rooms) pull it off well in
> my experience.

I hear this frequently on movie tracks. What I don't hear is anything close on standard 2-channel audio without any gimmicks used such as phasing. Reviewers wax loquacious at speaker systems all the time about soundstage wider than the speakers. Most of the time I think they're just dreaming. Maybe they're getting some modicum of reflections that give an overall impression on wider expanse. I don't like to have nearby side walls, so I don't get the influence.

dlr

[kene]

Re: So much of what's been said...


> A few
> rare recordings do seem to have more depth,
> but it seems to be only those exceptional
> recordings that let this come through.
> "The Trinity Sessions" by the
> Cowboy Junkies comes to mind.

Talk about a fantastic recording. My copy was stolen out of my car a couple years ago (along with my other 75 most-loved CDs); I was just about to burn backup copies of all my discs too! I still need to get it again, along with some 30 other discs.

> I have also never had width to the side
> beyond the left/right position of the
> speakers with the exception of certain
> limited frequency ranges that reflected off
> of a side wall that were related directly
> the the wavelength. False localization
> issues. I do not see how any 2-channel
> system could image to the sides beyond the
> speakers themselves if there is no
> reflection. I have never heard one to do
> that, anyway.

With purely acoustic recordings I haven't heard anything incredible. Most good recordings will give me just a wee little bit outside the width of my speakers, but almost never have I ever had my system in as good a room setup as I would like, so I don't rule out the possibility of side-wall reflections playing a role.

But there are some heavily-engineered discs out there that will employ certain tricks to generate illusions of sounds coming from farther beyond the speakers. Part of how they do this is by employing phase cancellations. Shoot a selected sound, say from the left speaker, and then shoot a phase-cancelling signal from the right, with appropriate sound muffling, to minimize/cancel what your right ear gets to hear. You can tell there are a lot of things that can go wrong so really not a lot of systems (in their rooms) pull it off well in my experience.

[kene]

Is it just me...


> It lacks that 3rd harmonic excess detail
> signature that most tweeters have in abundance.

> Dave

Or is there also quite an abundance of "Dave"s around here? "Ken"s too, enough that I sometimes think I need to find myself a handle. What's up with that?

[kene]

Think I figured it out.


> Yes, it does, because it supports the -60 db
> signal. That's the basis of my point, and
> Shannon.

Well, I'm not certain you saw how I had been framing the issue, which is fine because I finally remembered some of the reconstruction of amplitude with digital and realized that some of my suppositions were not applicable. This is why I keep saying I would like to work with the D/A conversion algorithms directly myself sometime. This was still worth discussing though.

Despite all that I rethink it all and the issues I see still end up collapsing into the more familiar "16bits => 100dB sampled at 22kHz just doesn't cover it" conclusion. The issue was never with the Shannon stuff you're referencing, at least as far as you've mentioned here; I've known all that stuff for years. Unless he was analyzing issues of digital audio back in the 50's. I wouldn't expect such. ;-)

Insofar as I'm reading you though, well...how would higher ambient noise levels enhance the ability to distinguish depth? If it were really about noise allowing the brain to exercise interpretive liberties in creating ambient cues that aren't really there then I would expect the presence of noise to uniformly instill all sounds with a similar sense of depth, even with purely artificial sounds that contain no spatial information whatsoever. At some point or another this noise should have a homogenizing effect which would impair the ability to resolve things as being closer or farther away. Now I've never listened to a "good turntable" so I don't know if maybe this is exactly what happens, so...well you tell me. Expound on how it might work.

[unknownuser]

Re: Vinyl Theories and other interesting diversion


>Does current digital have the ability to resolve a change in amplitude this small from a single 16-bit word?

Yes, it does, because it supports the -60 db signal. That's the basis of my point, and Shannon.


(Originally posted by: DDF)

[kene]

Re: Vinyl Theories and other interesting diversion


> I guess my earlier point went missed. The
> inherent resolution of any carrier mechanism
> is mathematically related to the SNR. See
> Shannon’s work from the 40s or 50s. Its
> pretty straight forward. SNR sets dynamic
> range sets resolution available. Doesn’t
> matter is its analog or digital.

Yes, this part is pretty straight-forward. What I'm trying to discuss is going a bit more in depth. What you've discussed so far is perfectly applicable for simpler waveforms where all harmonics are approximately equal in amplitude. The issue I'm talking about is if you have two signals, one at 0dB and another at -60dB, which would not be unreasonable for a good deal of ambient information that accompanies music we listen to, and attempt to represent it using the current 16 bit format, the individual words do not see two signals. It sees an absolute amplitude only. If you calculate how much the total amplitude will change as a consequence of the -60dB signal being removed you will see a drop of only 0.004dB. Does current digital have the ability to resolve a change in amplitude this small from a single 16-bit word? This is why I'd like to work with the algorithms myself, but my overwhelming suspicion is that digital won't come remotely close. What must happen instead is several words have to go by until the instantaneous amplitude of the larger waveform drops down to the viscinity of -60dB where the smaller signal can be resolved. This is a limitation of the digital format that does not apply to analog, and to me this rings as a critical factor. It also sounds almost exactly like what Jeff seems to be describing when he refers to "fractal" resolution in analog.