TOPIC:

I was curious as to the possibility of a plugin with a processing chain similar to the image linked below. There is a significant car audio community that would be interested in the ability to feed in stereo audio, create a L-R and R-L difference pair from that input, apply GEQ and delay the output from the input. This is of specific use as ambient rear fill on Sound Quality car stereo installations, and is a processing chain not currently available in a standalone product.

-Highly

Wow, highly, I was thinking the exact same thing! How about it folks, a rear processing plug-in (L-R, R-L) would be awesome. I could imagine apps for the home audio folks for this one, as well...

Thanks,

Greg

Interesting idea... What max delay are we talking about?

At a quick glance, I don't think I see a problem in this configuration, thing is it will require a new plug-in. So like with any project/plug-in we don't just build a plug-in based on the wishes of a single user. (miniDSP being a community)


Can you clarify what would the value for Car Audio users on such feature? That could help us realize if we should put it on our engineer schedule or not.

admin wrote:

Interesting idea... What max delay are we talking about?

At a quick glance, I don't think I see a problem in this configuration, thing is it will require a new plug-in. So like with any project/plug-in we don't just build a plug-in based on the wishes of a single user. (miniDSP being a community)


Can you clarify what would the value for Car Audio users on such feature? That could help us realize if we should put it on our engineer schedule or not.

Delay should be in the 20mSec range, optimally greater than the Haas limit. Adjustability +/- 5mSec would be more than adequate I believe.

As for the value for Car Audio users, there have been DOZENS of threads on the diymobileaudio.com forums relating to the use of rear fill for Sound Quality competitors to increase the apparent size and width of the image and to create a sense of space and ambiance. It would be difficult for me to gauge the probable number of users, but there has been significant interest in the concept, and your price point, processing power, versatility, and DIY nature would certainly garner more than casual interest. I am reasonably certain word would spread like wildfire if you were to make a plugin available. Numerous users have expressed interest in a device that would make such a setup possible without resorting to completely rearchitecting a system around the only processor that I know that performs such a processing chain; the JBL MS-8. It has other requirements that make it less appealing to a crowd of DIYers that already have 95% of what they are after in their current systems and that do not wish to run a center channel. Additionally your amplifier addon would make you a one stop solution, something no other vendor is in the position to realize.

I hope that helps to answer your questions...

-Todd

Thanks for the clarification Todd. You're bringing up very good points and sound like a convincing salesman to me!

Alright, let me talk to our engineer to see what could be done for this plug-in. We'll let you know what comes out of the talks, considering we already have a very busy schedule.

Tony

That sounds great. I anxiously await your findings!

In the meantime I have posted to the (DIY) forum to see what kind of interest this plugin generates. With a little luck we'll see some people chime in here to help you gauge interest.

-Todd

Todd,

A bit early to say but just out of curiosity, I built a template configuration to have a look at DSP requirements and here is the gist.

- the configuration you need can't achieve 20ms required, but only 15ms delay. That's because 2 x graphic eq actually take up a fair amount of processing.
- From my understanding of acoustic and what you're trying to achieve, here are my comments:

a) Providing you have identical set of speakers, you shouldn't need separate GEQ because you should actually apply the exact same eq to both speakers. Doing otherwise would change the sound stage and potentially create an imbalance.

b) L-R and R-L are actually the same. Just one is inverted i.e. - (L-R) = R - L

c) From our acoustic/speaker building experience, I'd say that 15ms isn't enough. 20 to 25ms is more like it to show a noticeable effect on the spacial effect. All this depends of your car though so i'd expect some margin...

d) So here is what i think makes more sense: Go mono for L-R, process it Band pass, process it Graphic EQ, delay it by a single delay around20ms or so, then split to 2 channels, each having a small delay to catch up small anomalies. Finally, invert one of the channel to make that L-R to a R-L. see a quick diagram of what I mean below.

Hope this makes sense

Overall I agree with your assessment of the functionality requirements. Normally in a room the listener is located not just equidistant to the speakers, but also at the same relative angle to the speaker. In a car that is seldom the case and we rely on EQ on each channel to correct the frequency response of the drivers relative to the listener. This capability is extremely important on the front stage to prevent frequency dependent image drift; the propensity for the center image to "pull" to one side or the other at specific frequencies due to the asymmetry of the seating position relative to the speakers. I do not know the degree of importance of that functionality in a rear-fill scenario. Having the GEQ in the mono portion of the chain will allow for voicing correction to the front stage, so that is a significant benefit, and the time correction for the individual L/R will help with keeping the image centered to the listener.

Just out of curiosity, is it possible to have a less-than-31 band EQ at work here? Likely bandpass frequencies of 200-3KHz would seem to limit the requirements for out-of-band adjustability and reduce the band count to 12-ish per channel. Might this free up enough processing capability to add limited stereo equalization in lieu of the single mono 31-band (most of which will never be leveraged)?

If not, I think the signal chain you have depicted should work quite very well indeed! I think I will be ordering a MiniDSP now so that I have some familiarity with the unit and am ready to implement/test this plugin (should it be developed). The MiniDSP is so extremely versatile that I will undoubtedly find uses for it either way!

Thank you SO much for your extremely timely responses to this query. I have to admit I have never seen this level of effort from any manufacturer of anything in response to a potential customer's inquiry. Truly a standard others should seek to emulate!

Thanks again!
-Todd

Todd,

In answer to your question about less band and still the ability of getting stereo, It won't work since it won't be freeing enough resources.

In the end, from my acoustic experience building speaker system & tuning PA, I actually don't think that you'd need stereo for the reasons I highlighted before. With the added fact that you end up with delay and phase inversion (giving you more than enough leaway), I can't see why you wouldn't be able to achieve your rear fill effect.

My 2cts.

No problem. Sounds like it's in good hands to me!

Just checking in to see if this one is likely to make the cut!

Thanks
-Todd

Todd,

It's indeed looking quite good so far. If everything going as planned, we should be releasing that new plug-in in the next few days.

DevTeam

That is great news, i'll be on the lookout for that plug in.

Guys, this is awesome, I'm a DIYMA member and I found this product through that forum. I bought a couple of boards and the L-R plugin and I can't wait to implement it. So, yes, highly is right about there being a market, and I'll be posting my use of this product in my DIYMA build log. Thanks guys!

Dan

So, little problem here. I can't get the rear fill plug-in to work. I know the miniDSP works. I have it hooked up on my bench playing normally with a 2-way plug-in, and it works on all four output channels. I'm using music that has L and R information. I can reflash the board with L-R while it's playing and it goes silent. Then I can reflash it again with the 2-way plugin and it plays. It doesn't matter which output channels I use, there's no signal on 1 & 2 or 3 & 4. I have also tried switching it to L+R so that I know there is musical information, and still nothing plays. Is there something I'm missing here?

Dan