How to find what music has stereo bass (with EasyEffects)

[olieb]

Below were Dr Toole's settings of his previous setup in California. The level settings of the SFM optimized subs alone were 0 dB left front, -6 dB right front, -12 dB left rear, -12 dB right rear. Each sub also has its delay and one PEQ attenuation filter. I doubt SFM optimized sub settings will work very well in general for stereo bass.

It will certainly not work, if you do not try. It is not that things will break.
I do not see a reason to assume the result of an attempt, in particular when it is obvious that there is something that could be missed by always summing to mono.
In the described situation with four subs a very simple and crude first try could be to route left channel bass to the left subs and right channel to right subs.
For mono bass that would change nothing, so with the flip of a switch you can always revert to your "optimized" solution.
For stereo bass one would need to adjust the level of uncorrelated ("side") signal such that the result is not disadvantageous.
Maybe one would find that this results in -∞ dB for the "side signal", or that every audible change that can be created is for the worse, maybe not.
And of course more sophisticated routing might be better necessary.

 

[j_j]

Something to remember about LP's. Rumble is most often strongest in the L-R sense, in other words, out-of-phase low bass.

 

[audiofooled]

First thing to figure out is how you deal with stereo flaws for the phantom center, both for close field and far field, for the low frequencies alike. Which also comes with a catch that left and right channel are equally contributing so that the cues are actually provided by the summation, again for the low frequencies alike. This is a real pain in the neck considering control bellow the transition region.

 

[levimax]

I have recently been playing around with moving from 4 subs to one big sub to 2 big subs co-located with the mains in order to get stereo bass. I tried to set it up so I could easily switch back and forth between stereo and summed bass but that part has proven to be problematic as well as bringing up some questions about how exactly sum to mono is executed. The problem with quick switching between stereo and summed mono bass is that when summed to mono the subs become louder (6 dB) which is clearly audible. It takes time for me to adjust the gain so comparisons are difficult but in some cases it seems like the summed bass sounds different. The question this raises for me is that how summed bass affects the crossover? Assuming a recording with stereo bass summed to mono then the signal on the sub side of the crossover is different that the signal on the mains side of the crossover. Not sure about audibility but it seems like it has to be sub optimal and I never see this issue mentioned. At this point I am preferring the stereo bass but of course there are some biases that could be in play.

 

[Chrispy]

Is NOBODY interested in stereo bass?

Like ULF somewhat a specialty endeavor?

 

[audiofooled]

I have recently been playing around with moving from 4 subs to one big sub to 2 big subs co-located with the mains in order to get stereo bass. I tried to set it up so I could easily switch back and forth between stereo and summed bass but that part has proven to be problematic as well as bringing up some questions about how exactly sum to mono is executed. The problem with quick switching between stereo and summed mono bass is that when summed to mono the subs become louder (6 dB) which is clearly audible. It takes time for me to adjust the gain so comparisons are difficult but in some cases it seems like the summed bass sounds different. The question this raises for me is that how summed bass affects the crossover? Assuming a recording with stereo bass summed to mono then the signal on the sub side of the crossover is different that the signal on the mains side of the crossover. Not sure about audibility but it seems like it has to be sub optimal and I never see this issue mentioned. At this point I am preferring the stereo bass but of course there are some biases that could be in play.

Stereo subs should sum to mono for the mono correlated part of the signal (and become 6 dB louder, independent of the frequency within their operating bandwidth determined by the crossover). For the decorrelated part of the signal they should also sum correctly as dictated by the signal, up to a point they are almost inaudible, pressure wise. But that's only part of the equation, taking rooms into account.

 

[krabapple]

Try this: Make a 50Hz tone with your favorite gadget. Phase shift it by 90 and 180 degrees in the opposite headphone. (No acoustic mixing needed.) Same level, of course, exactly.

Tell me these sound the same. Just go do it.

Room correction makes little sense above a kHz or two, but for the purpose of imaging stabilization, doing broadband correction of both channels (talking stereo for starter) for timbre (1/2 octave or so above 500Hz, along with standard room correction) based on ***THE DIRECT SOUND FROM THE LOUDSPEAKERS ONLY*** is a very good idea.

Long-term measurements that include the room acoustics are wrong above a a few hundred Hz. Of course, really bad room acoustics are just not very correctable, in particular specular reflections are the pits.

jj, what does 'long-term measurements' mean here?

 

[j_j]

jj, what does 'long-term measurements' mean here?

Power response estimate with pink noise, white noise, whatever, over a window more than 2 milliseconds at 20kHz, and not UNDER 200 milliseconds at 100Hz. The window *must* work according to cochlear dynamics to get the right answer. No options.

 

[levimax]

There is no such thing as stereo subs unless you want them to be +80hz woofers. And then work to integrate them (unless you don't deserve a basic ASR entry medal).

These are co-located stereo subs carefully integrated with the mains with flat stereo bass to below 17 Hz. I also have DIRAC DLBC which mono's the bass. It sounds good both ways .... the FR response with DIRAC is smoother on a graph but not particularly audible. Stereo bass gives a chance at envelopment i.e. AE but I seldom hear it on most recordings. Nice to have choices.

 

[pablolie]

These are co-located stereo subs carefully integrated with the mains with flat stereo bass to below 17 Hz. I also have DIRAC DLBC which mono's the bass. It sounds good both ways .... the FR response with DIRAC is smoother on a graph but not particularly audible. Stereo bass gives a chance at envelopment i.e. AE but I seldom hear it on most recordings. Nice to have choices.

I hope you're not claming 17Hz bass is directional and can be stereo.

Bass under 80Hz is not stereo ever period, although uncontrolled it may give you that misdirected illusion.

 

[levimax]

I hope you're not claming 17Hz bass is directional and can be stereo.

Bass under 80Hz is not stereo ever period, although uncontrolled it may give you that misdirected illusion.

It can be stereo in that the right and left channels can be different signals. Not sure about the psychoacoustics below 80 Hz and apparently it is not settled science.

 

[NTK]

I hope you're not claming 17Hz bass is directional and can be stereo.

Bass under 80Hz is not stereo ever period, although uncontrolled it may give you that misdirected illusion.

The audible sensation from stereo bass is not one of directionality (e.g. source location), but of auditory envelopment (a spatial sensation). There was some recent "high level discussions" (exchanges between experts/luminaries) on the topic. Here is an example post by J J:

Post in thread 'A Broad Discussion of Speakers with Major Audio Luminaries'

Apr 16, 2025

Sorry JJ but In small rooms the resonances dominate bass quality, and it turns out that prominent resonances behave in a minimum-phase manner, meaning that the steady-state frequency response in that frequency range is a reliable indicator of the potential audibility of those resonances and of the frequency and Q of filters to attenuate them - but only for a single listener. Multiple subs can actively manipulate room modes, which is a more challenging, but reduces seat-to-seat variations. Todd Welti elaborates on this in the upcoming 4th edition, but the basics are in earlier...

• j_j

• 

You are welcome to try out some synthetic test tones from this post of mine.

Post in thread 'A Broad Discussion of Speakers with Major Audio Luminaries'

Jun 20, 2025

For those interested in some contrived test signals, I followed Dr Griesinger's method and generated an example using narrow band noise (using 25 multi-tones), with each tone having randomly fluctuating phase. Basically the noise is a sum of tones generated by:

signal = Σ A_n * sin( 2π*f_n*t + ɸ_n(t) )​

The phase is randomly fluctuating in the order of ~0.5 Hz. An example of the ɸ_n(t) function is shown below (horizontal axis is time in seconds, vertical axis is in degrees).

Below are the spectra of the generated noise and their waveforms. The noise is centered at 50...

• NTK

• 

 

[pablolie]

It can be stereo in that the right and left channels can be different signals. Not sure about the psychoacoustics below 80 Hz and apparently it is not settled science.

It is absolutely settled "sub bass" is *not* directional. Give us a pointer to a source that says it's not. Whether it 80 or 90Hz or such there is silly debate about. But anything under 80Hz being directional (unless there are unwanted room interactions) is not based on any scientific source ever.

 

[levimax]

It is absolutely settled "sub bass" is *not* directional. Give us a pointer to a source that says it's not. Whether it 80 or 90Hz or such there is silly debate about. But anything under 80Hz being directional (unless there are unwanted room interactions) is not based on any scientific source ever.

See post #33 above by @NTK, there may be more to bass than "directional".

 

[j_j]

There is no such thing as stereo subs unless you want them to be +80hz woofers. And then work to integrate them (unless you don't deserve a basic ASR entry medal).

Sorry, that's not really correct, although "stereo" is not quite the right term. Please read some of the other discussions on the sensory effects of bass. No directionality, but there is a senses of width/space that simply can not be created with one woofer. That goes down to at least 40Hz, too.

 

[j_j]

It is absolutely settled "sub bass" is *not* directional. Give us a pointer to a source that says it's not. Whether it 80 or 90Hz or such there is silly debate about. But anything under 80Hz being directional (unless there are unwanted room interactions) is not based on any scientific source ever.

Directional? No.

Sense of space, yes. You're extending the old results to more than is appropriate.

 

[bmc0]

It is absolutely settled "sub bass" is *not* directional. Give us a pointer to a source that says it's not.

Incorrect. Here's one source. Also check the references.
As far as I'm aware, many who study concert hall acoustics agree that the interaural phase and level fluctuations that occur below 80Hz in such a space contribute to the spatial quality of the sound. There's less agreement on whether it's worth the trouble to try to reproduce the effect in small rooms.

 

[audiofooled]

Directional? No.

Sense of space, yes. You're extending the old results to more than is appropriate.

It is directional, at least with "supernatural" signals of sorts:

L:

R:

Phase:

In my room it is localized just fine, far right and then left, about half a meter outside of the loudspeakers respectively. Within stereo limitations, of course. IMO It's about system requirements, rather than auditory mechanism abilities.

 

[Hayabusa]

Try this: Make a 50Hz tone with your favorite gadget. Phase shift it by 90 and 180 degrees in the opposite headphone. (No acoustic mixing needed.) Same level, of course, exactly.

Tell me these sound the same. Just go do it.

I tried and indeed its audible.
But for 50Hz this is a 10Msec time shift which is not possible without a headphone as the ear to ear path time/phase difference is lets say 25cm which is +/- 0.8msec.
I also tried that time shift and that was not audible.

 

[olieb]

Incorrect. Here's one source. Also check the references.

Thanks for the link, looks carefully done and answers quite a few questions.
Seems the human hearing apparatus is able to localise LF sources if the sound is close enough to anechoic (outdoors) conditions.
But depending on the amount of reflections and the influence of room modes this ability breaks down
- to "sense of space" (AE) in concert halls (large reverberant space) and maybe in rather large and superbly treated listening rooms (fast decay)
- even more in small listening rooms or living rooms.

I would think that it will depend very much on the room whether it is better to optimise for smooth FR with mono managed subs or for AE with "subs" in individual channels.

I tried and indeed it's audible.
But for 50Hz this is a 10Msec time shift which is not possible without a headphone as the ear to ear path time/phase difference is lets say 25cm which is +/- 0.8msec.
I also tried that time shift and that was not audible.

I cannot confirm that. I did a quick and dirty test with in-ears and REW and to me there is a subtle but clearly audible difference even with 0.5ms delay at 50Hz (third octave pink noise as well as sine).