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Comprehensive Review: " APL1 " - Advanced DSP / EQ / Phase Correction Unit

133K views 1K replies 70 participants last post by  cycfari 
#1 · (Edited)
External link: APL1

Want to start off this review by saying that this is without doubt one of the better products I've come across for a long time. Many thanks to "Raimonds" here on the forum, the designer of this product - who introduced and let me demo this product.

APL1, basically an advanced equalizer which utilizes FIR (Finite Impulse Response). It can form any curve you desire with very few restrictions, in addition to that it also corrects phase deviations in all minimum phase regions.

Instead of reciting the entire spec I'll just copy/paste it from the official website.

APL1 – Unbeatable Quality in Pocket Size

APL1 is a FIR based 2 channel equalizer with 4096 coefficient FIR filters per channel allowing curve resolution of up to 6Hz. It is capable of creating any arbitary Amplitude Frequency Respone (AFR), Phase Frequency Response (PFR) or Delay Frequency Response (DFR) suitable for very detailed and accurate corrections and equalization in critical applications such as studio monitors, headphones and car audio systems.

USB connection allows the upload of correction filter files to APL1 unit even in the middle of a live performance without any disturbdances in sound. The unit can optionally have a 16 preset memory accessible trough an external, freely placeable rotary switch, excellent for car audio installations.
APL1 is available in three different configurations:

1. RCA model for car usage – 4 RCA connectors for analog in/out, 2 – for SPDIF digital coaxial in/out, 2 TOSLINK digital in/out

2. XLR model – 4 XLR connectors for analog in/out, 2 RCA– for SPDIF digital coaxial in/out, 2 TOSLINK digital in/out

3. XLR model with optional AES/EBU digital in/out - 4 XLR connectors for analog in/out, 2 RCA– for SPDIF digital coaxial in/out, 2 TOSLINK digital in/out; 2 XLR for AES/EBU digital in/out

Specifications:

*Number of processing channels: 2
*Resolution: 48kHz/24bits
*Frequency resolution of correction curve: 6 Hz, 4096 coefficients at 24 kHz bandwidth

*Inputs: 2 analog balanced, digital - SPDIF coaxial and TOSLINK optical, AES/EBU on order

*Outputs - 2 analog (XLR balanced), digital - SPDIF coaxial and TOSLINK optical, AES/EBU on order

*Input/output analog signal max levels: +10dBu (can be changed on order)
*Analog input/output connection types: RCA or XLR
*Analog input impedance: 10 kOhm
*Analog output impedance: 150 Ohm
*Common mode signal rejection (CMSR) of analog input – 90 dB
*Dynamic range (analog input/output):104 dBA.
*THD (analog input/output): 0,07%
*Signal delay: 1.6 ms (analog input/output), 2.4 ms (digital input/output)
*Control and upload interface: USB
*Interface computer system: Microsoft Windows
*Power: 6.5 to 16 V DC, 3.5 W.
*Dimensions 15х20х5.3 cm.
Let's begin with some pictures:

Good packaging...















Let's take a look inside:

















A little summary of the pictures. The components are high-grade as far as I can tell, ICs from Burr-Brown and ST. The circuit board is sturdy and it looks overall well engineered. I really like the USB connector, lots better than those small mini/micro USB connectors. Connections are gold-plated and feels sturdy, you don't break the board when you pull of those tight RCAs. Removable power connector for quick install/removal.

The impressive part is yet to come though!

Here's the software...



Does it look complicated or perhaps different? Let's "dumb it down" a bit.



A few notes here:

1. APL measures and applies a curve which YOU CHOOSE.

2. Any curve can be modified or created saved as a simple text file. APL will interpolate adjacent frequencies.

3. APL uses multiple measurement points to find out the true sound power response (direct sound + reflections) of the listening space. This is feature different from using pink noise and an RTA.


You can choose the "window" of the impulse response which basically determines the low-end accuracy. For car-audio use, Raimonds recommended 200ms length. You only need to choose the appropriate file and leave it at that. Nothing complicated.



Here's some "real life" use. Those who have read all my measurement guides and various threads involving DSPs should be used to my frequent use of graphs to display objective data.. Sooo - here's a few for you ;)

Initial setup - Simple 2-way passive + sub - No EQ (Crossovers at 100Hz 24dB/oct acoustic both ways). The null at 70Hz is a modal cancellation. Left/Right power response shown.



Previous setup - Basic EQ and a few shelf filters applied using a MiniDSP. Left/Right power response shown.



Some additional fixes after measurements with APL...



The APL software then calculates based on the correction and target response to give you this, (left channel shown / "semi-flat" setting):



Before I get into the subjective part. Let's continue with some additional software presentation:



This is a neat little "extra" program that calculates filters, target responses, EQ, corrections etc. It outputs your curve to a text file that APL software can read and apply in different ways. Of course you can make one for each channel.

*Gain 20dB +/-
*Q from 0.1 to 100
*Center freq from 5-48000Hz.
*Low/High shelf filters.
*Low/high pass filters.

Pretty neat. There's a large room for customization here.


Here's the actual software to hardware interface:



You can store 16 presets in the unit and it only takes a second to shift between different settings. You just choose the *.fir file generated by the APL software and import it into this interface and you're done. Enjoy ;)

As I always do I like to confirm results or at least compare. Before using APL I used RoomEQ to a large extent (it still very useful, don't get me wrong). Again, even if you're not that accustomed to measuring you probably know of some of the procedure involving it, you basically measure around your head and average it together. APL is using a different method. With APL you measure the entire listening space, not just around your head. As a result the "ordinary" method using RoomEQ (or some other measurement program) differs from APL's result. When I first noticed this, I was skeptical because I always found my method quite accurate and correlated well with what I heard...

The thing I first noticed was that APL's version of flat didn't at all sound "flat", as in "RTA-flat". This made me curious to see how APL derived and displayed the curve. Below are results from RoomEQ using spatial average measurement method (headspace), using RTA and Noise with infinite averaging method.







Well, this is interesting indeed. "APL Flat" isn't actually "RTA-Pink Noise flat". If you were to use white noise as excitation signal, the results are fairly consistent with "flat". Using pink noise, it does create a downwards tilted curve explaining how the difference between "flat" and "flat". Another interesting thing is that the right side (passenger side) is lower in amplitude than the left side. This is consistent with the listening experiments I did when I derived my "house curve/target response" in RoomEQ.

And... thirdly, look how good the curves sum. A testament that APL indeed performs proper phase correction between left and right.

What does this mean? It means that APL does indeed derives data and compensating correctly and it correlates exactly with what we hear.

Conclusion & Subjective analysis

*This is a very powerful unit, very different from the EQ available in the DSPs available for car use. Different in a good way, it can do things any "normal" DSP can't and it's easy and straightforward to use.

*T/A and L/R EQ issues are gone with this unit. The acoustic center is perfect, even a simple 2-way passive system like mine sounded like a competition grade car. Depth is improved subjectively. Everything sounds clearer, more transparent and so easy to listen at. No annoying frequencies that stand out, even crappy recordings that normally is un-listenable suddenly becomes tolerable. The center focus is insane, the up-front bass is improved by an enormous amount (in this car). With a crossover point at 100Hz/24dB both ways, the sub was impossible to localize with any material (any amount of processing won't fix resonances in the car or non-linear distortion so take that into account) . The image stayed up-front and kept staying there.

(I am aware that the result varies, if you already got an audiophile grade competition car the improvement is less than with a "normal" install but in my opinion it's still worth every penny. It's that good.)

*My noise-free preamp is still broken so I couldn't run I/O tests but I'll tell you, it's transparent as far I can hear. No noise whatsoever, I even maxed volume with a 0 bit track but nothing. Couldn't hear any coloration with the unit in "raw-passthrough".

*This unit does NOT replace an ordinary DSP, in fact you need an ordinary DSP as well. You place the APL1 unit before the DSP - 2RCA's in - 2 out. Not more complicated that that. If you don't own a DSP and is interested in this product, I recommend using it together with a MiniDSP (among the cheapest and best on the market).

*Support and feedback is great! The value in this is enormous with these types of products.

Overall a 10/10 score from me. Will use it in my main competition build...

Link to Raimonds profile; Car Audio | DiyMobileAudio.com | Car Stereo Forum - View Profile: Raimonds
 
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#572 ·
Re: Comprehensive Review: " APL1 " - Advanced DSP / EQ / Phase Correction Unit

Thank you Raimonds.. Question then becomes if a person wants to sacrifice the FIR taps for a little extra resolution. I'd vote no at first at least.


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#576 ·
Re: Comprehensive Review: " APL1 " - Advanced DSP / EQ / Phase Correction Unit

SubterFUSE has a nice way to make inverse filters with smaart
If someone wants the free way you can use rephase , click on compensate mode and draw the responce with the IIR eq and export the eqs as biquads (if you have minidsp)
Otherwise you could write down the values from rephase and copy them into your dsp manually.

It's pretty sweet. Just be careful of inverse filters with adding boost. I would draw the responce at the bottom line on the frequency responce so it only cuts in the majority of the filter
 
#577 ·
Re: Comprehensive Review: " APL1 " - Advanced DSP / EQ / Phase Correction Unit

So, I'm at a show and don't have much time to check, but I think I mentioned that I'd be willing to drive to NC to help people learn their APL...

So here's the deal, I get home(TX) on the 19th, and will be home until the 7th. The bad news is that the Miata will go into the shop to repair the hail damage on the 20th and it could be there the entire time I'm home, they say it'll only be 9 days, but I don't trust that. So that doesn't leave me any time to travel with my car and APL.

However! When I hit the road again, I'll be going to Williamsburg, VA for two weeks, on 5/10-5/14 I could do one-on-one teaching sessions in the evening. I can do the same, in the same location, on 5/22-5/23. But you MUST bring your car to me, AND already have your APL1 installed and ready to tune. I'll have the software, laptop, and mic to tune with. Also, the bar just off the course is awesome and I'll buy the first round!

Also, are there any other APL owners in the country who have a unit and don't really know what they are doing? If so, speak up! My tour might be coming to your area!
 
#647 ·
Re: Comprehensive Review: " APL1 " - Advanced DSP / EQ / Phase Correction Unit

So, I'm at a show and don't have much time to check, but I think I mentioned that I'd be willing to drive to NC to help people learn their APL...

So here's the deal, I get home(TX) on the 19th, and will be home until the 7th. The bad news is that the Miata will go into the shop to repair the hail damage on the 20th and it could be there the entire time I'm home, they say it'll only be 9 days, but I don't trust that. So that doesn't leave me any time to travel with my car and APL.

However! When I hit the road again, I'll be going to Williamsburg, VA for two weeks, on 5/10-5/14 I could do one-on-one teaching sessions in the evening. I can do the same, in the same location, on 5/22-5/23. But you MUST bring your car to me, AND already have your APL1 installed and ready to tune. I'll have the software, laptop, and mic to tune with. Also, the bar just off the course is awesome and I'll buy the first round!

Also, are there any other APL owners in the country who have a unit and don't really know what they are doing? If so, speak up! My tour might be coming to your area!

I'd be interested in learning about it. I'm up in PA, but could come down to VA if that works.
 
#579 ·
Re: Comprehensive Review: " APL1 " - Advanced DSP / EQ / Phase Correction Unit

I'll be in Portland this summer, but I won't have my car with me. When I'm touring I'm driving a Peterbilt with a stock system that is so terrible I'd rather listen to headphones.

I have family in Seattle, and might make it up there this winter wit the car...
 
#580 ·
Re: Comprehensive Review: " APL1 " - Advanced DSP / EQ / Phase Correction Unit

I'll be in Portland this summer, but I won't have my car with me. When I'm touring I'm driving a Peterbilt with a stock system that is so terrible I'd rather listen to headphones.

I have family in Seattle, and might make it up there this winter wit the car...
Well keep me informed. Ill prob have a ddrc24 by then. Maybe u can help me tune that :)

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#585 ·
Re: Comprehensive Review: " APL1 " - Advanced DSP / EQ / Phase Correction Unit

The same help in Europe/scandinavian countries. I can assist everybody in using apl in the best way.

Sendt fra min GT-I9505 med Tapatalk
 
#586 ·
Comprehensive Review: " APL1 " - Advanced DSP / EQ / Phase Correction Unit

Clay helped me tune my APL1 today. We did not have a lot of time but I just wanted to get a general idea for what it can do.

The improvement in tonality was impressive. Especially in the midbass and sub bass response. It made my bass sound louder and cleaner at the same time.

We ran into 1 problem. Before taking the measurements we loaded my current competition tune into the Helix DSP Pro. Then we measured with APL Workshop and calculated the filters. We applied the filters to my APL1 and listened. The tonality improved but my center image got moved from perfect center to about 12 inches left of center with the APL1 activated.

Why would the APL make my center image move to the left? Did it measure my right side as being louder than the left and then overcompensate?


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#588 ·
Re: Comprehensive Review: " APL1 " - Advanced DSP / EQ / Phase Correction Unit

Elgrosso is right. The reason is that apl attenuates the amount of acoustic power from both fronts to an equal value. Very precisely. It is difficult to achieve this result with another means. Now it is time to make new time alighnment, as out of two channels, that which located more closer to a listener, sounds more loud. Distance now begins to play a dominating role in moving the scene due to energy dissipation in the air.

Regarding tonality - it is the same now after the apl run. If you made some EQ before this with Helix DSP, you was not able to get it equal for these two channels. It means again - need for TA. By definition, it is not possible in practice to get the same results with a unit having 31 taps against 4096 availabe available for apl1. Corrected tonality in the first turn means less masking of sound by each other. That is why people are typically amased listening apl result for the first time.

Last, but not least - solving of minimum phase problems with the help of apl technology. Solving this results usually in better tonality, and as a result - need for new TA.

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#589 ·
Re: Comprehensive Review: " APL1 " - Advanced DSP / EQ / Phase Correction Unit

So do I need to listen to the new APL tune and adjust the delay to move my center stage back into the correct location?

After that, do I measure with workshop again? Do I measure with the APL filters active or bypassed?

Claydo will attest that before applying the APL filters my tune in the Helix DSP was very good. After APL it was better in tonality but worse in soundstage and imaging.


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#590 ·
Re: Comprehensive Review: " APL1 " - Advanced DSP / EQ / Phase Correction Unit

Bypass is all switched off. So no meaning. It is enough just with one run of the apl test. Avoid bypass and make TA

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#591 ·
Re: Comprehensive Review: " APL1 " - Advanced DSP / EQ / Phase Correction Unit

The left and right sides are measured independently, aren't they? Sorry I missed that when you guys were doing your thing with the mic.


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#592 ·
Re: Comprehensive Review: " APL1 " - Advanced DSP / EQ / Phase Correction Unit

Right, sepatately. But after apl run they must play exactly the same. You can repeat the test with uploaded filters in order to check how apl1 fits your target curve for both front channels. It is very helpfull to plot the result of the second test along with the target curve on the same plot.

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#593 ·
Re: Comprehensive Review: " APL1 " - Advanced DSP / EQ / Phase Correction Unit

Right, sepatately. But after apl run they must play exactly the same. You can repeat the test with uploaded filters in order to check how apl1 fits your target curve for both front channels. It is very helpfull to plot the result of the second test along with the target curve on the same plot.

Sendt fra min GT-I9505 med Tapatalk

Sounds like then a good thing for the Helix DSP since you can link sets of drivers. So link left side then link right side, then set TA after the APL1 tune to center image. Crucial timing being done prior being down the sides.. Left tweeter to mid to midbass to sub.


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#594 ·
Comprehensive Review: " APL1 " - Advanced DSP / EQ / Phase Correction Unit

I was really impressed with what I heard this weekend in Clay's car with the different APL1 curves. Probably the best coherence from top down that I've heard in that car. Nothing stood out as an issue. Excellent tonality.


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#595 ·
Re: Comprehensive Review: " APL1 " - Advanced DSP / EQ / Phase Correction Unit

Thanks Scott!

I had my best results setting up everything before the apl measurements. If you have any, I mean any errors before apl, the apl tune will make them stand out and smack you.....lol. So pre apl, you'd better have it right, or its not going to work. I wouldn't change anything after the apl corrections, but if the apl showed errors in my setup, I would simply recognize what it showed me with the sound, revisit that area with the apl in bypass, then run a new apl measurement with my dsp setup corrections already applied, but always measuring the system with the apl in bypass, so im measuring the basline dsp settings, and not previosly applied apl corrections. I feel that adjustments after the apl corrections taint it's "magic", and my testing confirmed this. So any miscues in your post apl corrections are typically manual setup mistakes in your dsp........
 
#597 ·
Re: Comprehensive Review: " APL1 " - Advanced DSP / EQ / Phase Correction Unit

Guys..... I have a lot to add but don't have the time to type it up right now.


I took my car to a show this weekend and used the APL1 tune, but with some minor corrections that I made to fix the imaging problem.

I took 1st place in both of the formats, and several people that have known my car well all said I have the best tune in the car that I have ever had.

I have some pictures of the response in the car to share, also.... so we can see what the APL did and how I fixed it to get through my competition. I'm eventually hoping to understand what we did wrong to make the APL mess up my imaging so much, but that will have to wait until I have enough time to type a full report.

The bottom line is that my car does sound better than it ever has before, now that I have activated the APL1.
 
#598 · (Edited)
Re: Comprehensive Review: " APL1 " - Advanced DSP / EQ / Phase Correction Unit

Congrats John! Apl for the win....lol. What did ya do, just correct the stage shift after the apl corrections? Well.....just remembered you stated you didn't have time to tell the whole story.......so it can wait....lol.

I'm glad you're liking the results tho......I love what it did in my car, and the ease of applying new curves over top of the correction files absolutely knocks it out of the park for me. I was hoping it would work out for ya in the audi, and when I heard what it did for your sub/midbass transition, I knew it was gonna be phenomenal once the staging was fixed. I hope you get to try what I sent you in pm, just out of curiosity if nothing else, because that path (as simple as it sounds) made my car sing like it never has.
 
#610 ·
Re: Comprehensive Review: " APL1 " - Advanced DSP / EQ / Phase Correction Unit

Congrats John! Apl for the win....lol. What did ya do, just correct the stage shift after the apl corrections? Well.....just remembered you stated you didn't have time to tell the whole story.......so it can wait....lol.

The only changes I made was to the EQ in the Helix DSP. The APL1 messed up the EQ balance left to right side, so I just went into the Helix and quickly fixed it so that the left and right speakers were playing equal.

Once I did that, my center image was perfect. Left side and Right side images were also perfect, and moved outside of the pillars to the side mirrors.

The left-center and right-center images were OK, but they did move around based on frequency. I attribute this to the passive crossover between the tweeter and midrange drivers, and the lack of independent EQ on them.


I'll post measurements when I can find the time.
 
#600 ·
Comprehensive Review: " APL1 " - Advanced DSP / EQ / Phase Correction Unit

Looking around for what I can sell for the last bit of coin to put my order in. Lawn care? I can't part with my little JL 12TW1 but might have to.


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#606 ·
Re: Comprehensive Review: " APL1 " - Advanced DSP / EQ / Phase Correction Unit

Looking around for what I can sell for the last bit of coin to put my order in. Lawn care? I can't part with my little JL 12TW1 but might have to.


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LOL, ive been reading and re reading this thread over the last couple of days, and im in the same boat...wondering how much of the stash i am willing to part with. Anyone want an ms8?
 
#601 ·
Comprehensive Review: " APL1 " - Advanced DSP / EQ / Phase Correction Unit

I will say from John's statement that delay steepens the phase response, if that's the correct appropriate terminology, I'm going to try different delay settings and play with incremental phase to see if I can make the subs and midbass have more "in-phase" bandwidth in their crossover region. Unfortunately no time to try this in room EQ wizard as it's not real time.


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#603 ·
Re: Comprehensive Review: " APL1 " - Advanced DSP / EQ / Phase Correction Unit

It's a great unit Scott, I think it would improve anyone's sound.......

Even mine right? LOL!!!!! But yeah what it's done for yours is amazing I have to admit.


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#605 ·
Re: Comprehensive Review: " APL1 " - Advanced DSP / EQ / Phase Correction Unit

Guys, try TDA APL for optimisation of TA. Believe me, nothing is more evident in results. Delays could be made just within apl techology pack. If you use ConneqC1, you are not limited more to 10-15 msec like other DSP's. Mine is more than 50 msec now for the front channels. It was necessary to keep everything comming simultaniously to the listening point.

Congratulations to subterFUSE. Great results.

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#607 · (Edited)
Re: Comprehensive Review: " APL1 " - Advanced DSP / EQ / Phase Correction Unit

Guys, try TDA APL for optimisation of TA. Believe me, nothing is more evident in results. Delays could be made just within apl techology pack. If you use ConneqC1, you are not limited more to 10-15 msec like other DSP's. Mine is more than 50 msec now for the front channels. It was necessary to keep everything comming simultaniously to the listening point.

Congratulations to subterFUSE. Great results.

Sendt fra min GT-I9505 med Tapatalk
I have TDA, and tried it a couple times with mixed results. I attribute the inconsistencies to the Operator (me), rather than the tool. I'm quite sure I certainly don't understand all that's going on in the software. TDA would be a very good candidate for in-depth youtube instructional video. I have no doubt that in the right hands, it can make alignment a very simple task. Reading over this doc again it's starting to make better sense.. The main measurement screen interface is where I got stuck last time though..
http://aplaudio.com/downloads/Introduction-to-TDA.pdf
http://aplaudio.com/downloads/TDA-Installation-and-Quick-Start-Guide.pdf
 
#608 ·
Re: Comprehensive Review: " APL1 " - Advanced DSP / EQ / Phase Correction Unit

It could not be a mess if you place the mic at exactly the same position. Software interface is easy to understand. The latest versions give you more detailed information. So, what's the problem? My suggestion is not to move a mic if you play with TA settings or optimizing subwoofet location.

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#609 ·
Comprehensive Review: " APL1 " - Advanced DSP / EQ / Phase Correction Unit

It could not be a mess if you place the mic at exactly the same position. Software interface is easy to understand. The latest versions give you more detailed information. So, what's the problem? My suggestion is not to move a mic if you play with TA settings or optimizing subwoofet location.

Sendt fra min GT-I9505 med Tapatalk

No problem really. Just need to practice with it. Mic for this would always be stationary at the headrest. And agreed, it's certainly easier than generating IR plots in Room EQ Wizard which requires a reference loop-back from the system or sound interface. And the visual plot it generates is by far easier to interpret, even for subwoofer timing which is sketchy at best if even possible with impulse response.


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