HT acoustics and the Benefits of better speakers in stereo and multichannel audio

[tomtoo]

That option was a bit of hyperbole but a surprisingly decent impression of an open air concert is possible. Defined spaces are easier.

But you would need new recordings. Dont get me wrong but at the moment i dont get the sense of changing one fake to another. Maybe fun thats ok. But i not see at the moment that more speakers uplift my fun.

 

[tomtoo]

Dont get me wrong, i like my HT sound for movies. But when i listen to stereo recordings, i always listen to the two main speakers.

 

[pozz]

@Thomas savage I can't give you a a direct answer, but I can give you the next best thing from Francis Rumsey, one of the leading researchers in spatial audio:

• (2014) Francis Rumsey - Spatial Audio: Reconstructing Reality or Creating Illusion?

The main finding is that timbral accuracy is the most important factor in multichannel blind testing for both experienced and naive listeners (experienced=sound engineers, naive="some punter you found on the street", according to Rumsey). Timbral accuracy is more important than a sense of spatial envelopment, which in turn is more important than imaging accuracy (phantom source localization). This suggests that loudspeakers should have flat on-axis response and consistent directivity, in line with Toole's research.

@tuga As you say, there's a sharp difference between multichannel recordings like stereo or 5.1 and accurate soundfield reproduction, which can't be done with conventional loudspeakers or rooms. The question to ask is when that stops mattering perceptually and what kind of system is sufficient. I don't think there's a satisfactory answer for that yet.

Rumsey does make these points based on listening tests:

• When using a ring of loudspeakers around a listener and playing decorrelated noise, if 90 degrees of that ring is active in front of the listener, then the sense of envelopment is around 80% (100% being the same as a true diffuse soundfield, like being in a field out in the country, hearing mostly distant noises). From the same experiment, having 3 loudspeakers across the front is sufficient for reproducing the same effect.
• 5 channels positioned according to the current standard is sufficient to produce the sense of a diffuse soundfield (i.e., you can't localize the loudspeakers and increasing the number of channels doesn't add to the sense of envelopment).

This also suggests that wide directivity loudspeakers are preferable. Narrow directivity speakers, besides creating a very narrow listening position, will produce very coloured reflections and will be unable to use the room's energy to add to the spatial impression.

Hilariously, Rumsey calls NHK 22.2, Atmos and Auro 9.1 systems "advanced stereo" or "extensions of conventional stereophony". It's completely true if you know how these systems work. What they do is multiply the number of channels and use the same amplitude/timing differences as stereo to position phantom sources. This doesn't get you any closer to soundfield reproduction, as is done in wavefield synthesis.

 

[tuga]

This also suggests that wide directivity loudspeakers are preferable. Narrow directivity speakers, besides creating a very narrow listening position, will produce very coloured reflections and will be unable to use the room's energy to add to the spatial impression.

I agree that wide dispersion will increase the sense of envolepment or immersiveness.

But with recordings of live music performed in natural acoustic environments you are overlaying the acoustic qualities of your room over the ambience cues in the recording. This affects imaging and the recreation of the soundscape captured by the mics.

Ultimately it's all a matter of taste, whether you like narrow- or wide-directivity, a livelier or deader room, two-channel vs surround or ambeo.
They all have advantages and shortcomings.

 

[Erik]

Upmixing 2-channel is wishful thinking...

In many cases it sounds better than the original 2-channel recording, though. Sometimes even better than the original multichannel version of the same recording. There is a study on that too.

https://asa.scitation.org/doi/10.1121/1.2385043

 

[richard12511]

Maybe i see thing's to easy.
But if i listen to live music it's usually in front of me. The Drums are not playing behind me. So i not see why multichannel should give me a better impression.

It's actually impossible to recreate a live event with just stereo. You have to have speakers behind you if your goal is to recreate a live sound.

 

[tuga]

In many cases it sounds better than the original 2-channel recording, though. Sometimes even better than the original multichannel version of the same recording. There is a study on that too.

I wish people would stop using silly preference studies...

 

[tuga]

It's actually impossible to recreate a live event with just stereo. You have to have speakers behind you if your goal is to recreate a live sound.

Not just behind but around you and in an anechoic room.

 

[kevinh]

But you would need new recordings. Dont get me wrong but at the moment i dont get the sense of changing one fake to another. Maybe fun thats ok. But i not see at the moment that more speakers uplift my fun.

So one of the techniques that companies can use is to model a space, such as a concert hall or a Jazz club. JVC did this long ago, They measured different venues and built in a transfer function for each venue.

If you had a closed mike'd recording, then applied the transfer function to this recording with little/ no reflection information that give a sense of an acoustic space, then you have a recording that will sound more like live music. the purpose of the speakers other than the mains is to provide the reflected sound field.

OTOH, if one were to record using an omni directional mic in a real acoustic venue the microphone would capture the direct sound and the reverberate sound. Then you have the rom acoustics and decay rate of the room.

Most people have untreated listening rooms so the room acoustics problems is much bigger than the other effects IMO.

 

[jjk]

I agree with Kal.
I also agree with Toole who is very clear on this.
MCH is better.
Upmixing when done well is better. JRiver does a very good job of this.
If you need an example of modern rock music in MCH, Steven Wilson is the master. Bluray recording at 24/96 5.1. Previously with Porcupine Tree on BR/DVDA. DRs are in the 15s.
Reference: Hand.Cannot.Erase or To The Bone (SW)
Live Recordings as well: Home Invasion and Anesthetize (PT), among others
Stay safe.

 

[tecnogadget]

Not just behind but around you and in an anechoic room.

No need for such deployment of resources.
You can trick your ears and brain with far less than that. The auditory system is such a beauty

 

[M00ndancer]

Recorded Live Concerts is one, hearing the "room" is another and soundtracks/music from movies.

 

[tuga]

No need for such deployment of resources.
You can trick your ears and brain with far less than that. The auditory system is such a beauty

I prefer to be tricked by a single pair of speakers and if possible a real-stereo recording not a stereo mix.

It is likely that a real-stereo multi-channel recording will beat this but there isn't a lot of material available, such a system is expensive and you need a big room.
In my opinion "processed" 3D audio, like 3D video, is a gimmick but some people seem to enjoy it.

 

[Kal Rubinson]

Indeed they are. Especially spaces like small jazz clubs.

Sure. Churches and concert halls are relatively easy by now as are live performances in stadiums. Open air is still tough but I am not that much into marching bands.

 

[Kal Rubinson]

I prefer to be tricked by a single pair of speakers and if possible a real-stereo recording not a stereo mix.

Yeah but, nice as it can be, it no longer fools me.

It is likely that a real-stereo multi-channel recording will beat this but there isn't a lot of material available, such a system is expensive and you need a big room.

All that's relative, IMHO. I have a substantial library and two suitable systems.

 

[Kal Rubinson]

But you would need new recordings.

Of course.

Dont get me wrong, i like my HT sound for movies. But when i listen to stereo recordings, i always listen to the two main speakers.

I like my multichannel system for music. But when I listen to stereo recordings, i always listen to the two main speakers.

 

[pozz]

I wish people would stop using silly preference studies...

I'm surprised you haven't looked at the underlying research. Preference studies fall into the same type research done in all controlled studies in social science and psychology. Set up a situation carefully enough, and human behaviour falls into repeatable patterns. It makes the engineering simpler by defining the limits of perception and, accordingly, the design parameters.

But with recordings of live music performed in natural acoustic environments you are overlaying the acoustic qualities of your room over the ambience cues in the recording. This affects imaging and the recreation of the soundscape captured by the mics.

This is a good example of the limits of perception. What you're capturing is not the space, but the pressure fluctuations at the points where the microphones are located, according to their polar sensitivity. You're then reproducing the pressure fluctuations without directional information through loudspeakers, which are coupled to the room they play in. And yet the end result still sounds good.

The situation isn't simplified by using loudspeakers with restricted directivity or dead rooms given the way that you're capturing or synthesizing the soundfield in the first place. There are aspects of playback which you simply cannot control. But you can, however, use their characteristics to your advantage.

Not just behind but around you and in an anechoic room.

This ambisonic setup for example isn't the definition of soundfield accuracy. It has two main advantages besides the ones offered by other multichannel systems (no reliance on speaker location or discrete channel count, so you can input any format you like) and many disadvantages (small sweet spot, fuzzy or smeared imaging, timbral inaccuracy and spatial aliasing), even in anechoic circumstances.

In all other situations reflections are integral to the playback system by supplementing the distribution of spatial energy through acoustic phantom sources and can be controlled through treatment.

The main caveat, or frustration, I guess, is that you really can't take full soundfield accuracy as your goal. None of the known system configs really for allow it. Even with that in mind, I'd really like to hear the WFS system at EMPAC one day.

 

[tuga]

Yeah but, nice as it can be, it no longer fools me.

All that's relative, IMHO. I have a substantial library and two suitable systems.

Not everyone has a thick wallet...

 

[Kal Rubinson]

Even with that in mind, I'd really like to hear the WFS system at EMPAC one day.

Me, too. I have already made some inquiries.

 

[tuga]

I'm surprised you haven't looked at the underlying research. Preference studies fall into the same type research done in all controlled studies in social science and psychology. Set up a situation carefully enough, and human behaviour falls into repeatable patterns. It makes the engineering simpler by defining the limits of perception and, accordingly, the design parameters.

This is a good example of the limits of perception. What you're capturing is not the space, but the pressure fluctuations at the points where the microphones are located, according to their polar sensitivity. You're then reproducing the pressure fluctuations without directional information through loudspeakers, which are coupled to the room they play in. And yet the end result still sounds good.

The situation isn't simplified by using loudspeakers with restricted directivity or dead rooms given the way that you're capturing or synthesizing the soundfield in the first place. There are aspects of playback which you simply cannot control. But you can, however, use their characteristics to your advantage.

This ambisonic setup for example isn't the definition of soundfield accuracy. It has two main advantages besides the ones offered by other multichannel systems (no reliance on speaker location or discrete channel count, so you can input any format you like) and many disadvantages (small sweet spot, fuzzy or smeared imaging, timbral inaccuracy and spatial aliasing), even in anechoic circumstances.

In all other situations reflections are integral to the playback system by supplementing the distribution of spatial energy through acoustic phantom sources and can be controlled through treatment.

The main caveat, or frustration, I guess, is that you really can't take full soundfield accuracy as your goal. None of the known system configs really for allow it. Even with that in mind, I'd really like to hear the WFS system at EMPAC one day.

The spherical array of speakers makes sense if you use one speaker per channel not for some algorythm to generate a mish-mash fake illusion of immersion from a 2, 5 or 7 channel recording.