# Experience with APL1 sound corrector?



## Alextaastrup (Apr 12, 2014)

Found this link: 

Acoustic Power Lab :: Home 

describing sound processors from the Acoustic Power Lab. Does anybody have any practical experience with it?

According to the manufacturer this device has won different competitions in Europe. Looks promissing, but seems to be lacking some smart features as bluetooth, crossover, etc. As I understand the philosofy of the company - to produce a really audiophile unit of minimalistic design comprising only what is neccesary to produce high sound quality.

The „Pro Sound News Europe” trade journal lists SPFR (sound/acoustic power frequency response) correction technology as one of the three leading innovations in the field in Europe. The invention was awarded the Excellence prize by the AES in New York, 2007. In 2010 the author developed an alternative technology version for application in car audio systems. The car equipped with that solution earned “best sound” at the Salzburg EMMA-2012. Latest news – 2 first places at EMMA Eurofinals in SQ and MM in March 2014.

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.

Specifications:
•	Number of processing channels: 2
•	Resolution: 48kHz/24bits, digital input - uptil 96kHz/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.

As I understand, it is not on ebay yet, but could be purchased from the company link. Any ideas?


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## Alextaastrup (Apr 12, 2014)

It seems to be a right time to exchange practical experience of APL1 application as more and more SQ-enthusiasts became an owner of such a device.


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## Alextaastrup (Apr 12, 2014)

Alextaastrup said:


> It seems to be a right time to exchange practical experience of APL1 application as more and more SQ-enthusiasts became an owner of such a device.


Recently I have installed 3-way system in my car. It took less than one hour to test and tune it. Now I am enjoying music  instead of a nightmare of the time consuming tuning process. Really very powerfull device!








This is my front before tuning. Orange line on this first pisture - desired target curve.









And finally - result of tuning by APL1 sound processor. Deviation between the front channels is below 2 dB, which might be considered as acceptable. Comments?


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## crazhorse (Mar 9, 2010)

Looks good Alex........ still in the process of setting up/tuning mine. Replaced my tweeters and awaiting a new amp for my midrange. Hopefully I'll have it all setup soon.
Did you leave the setting at -6db for the upper and lower ? Also which wave did you use 50 100 or 200 ?


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## crazhorse (Mar 9, 2010)

Heres a sweep I took the other day of my system...








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## Alextaastrup (Apr 12, 2014)

You'll have problems above 7kHz, if you will use -6dB limitation. 80 and 180 Hz have also problems due to this limit (look on the target curve). With your tweeters I would rather recommend -18kHz. Wave 50 is fine. I used to switch it only when connecting sub and woofer, but this will be not so accurate at higher frequencies.

Remember to use a calibration file for your mic. It has changed the whole picture drastically in my car.


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## crazhorse (Mar 9, 2010)

I'll give it a try with those suggestions... working on some ta issues as well


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## crazhorse (Mar 9, 2010)

I replaced my pdx5 powering my mids for a mosconi one (230 x 2) ... did a workshop sweep at lunch today








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my tweeters fall off like rocks, not sure if its them being off axis in the doors or what....


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## Alextaastrup (Apr 12, 2014)

Where exactly your tweeters are placed?


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## crazhorse (Mar 9, 2010)

In the stock pods at the top front of the doors


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## Alextaastrup (Apr 12, 2014)

Seems OK. I had tweeters in almost the same position, but directed almost back. Never had issues. What about this stock grid? Couldn't it give off-axe problems - looks rather tight. Let APL1 solve this problem with its powerfull equalisation. Looking forward to see corrected curve


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## crazhorse (Mar 9, 2010)

Well the tweeters have grills and the speaker pods have grills as well... So double grilled.. But I think I tried with the pod grills off and it didn't make much of a difference I'll try remeasuring to make sure...


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## Alextaastrup (Apr 12, 2014)

Some new test results obtained with the help of TDA-software from the Acoustic Power Lab are presented below. 

First - Response of the left channel to the sweep signal.









How APL1 solves minimum phase problems could be seen from the next pictures:

Before (without APL):












And after APL1 was switched on.








Be aware that I am using a passive crossover for the front speakers, so time alignment bwtween tweeters, mids and woofers is not possible by ordinary means.


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## crazhorse (Mar 9, 2010)

I have played with the tda software some.... Not sure if my laptop/mic is wacky or the surrounding noise is interfering. But I can take a measurement then take another right after and the results are very different... This is making no changes just doing another sweep.


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## crazhorse (Mar 9, 2010)

Im not sure but if I'm not loading the .fir files correctly or what but after measuring and using aplconfig to send the files to the unit before and after measurements are the same... unit has power, led indicators work and it is detected when I connect to it to load the files........


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## Alextaastrup (Apr 12, 2014)

crazhorse said:


> I have played with the tda software some.... Not sure if my laptop/mic is wacky or the surrounding noise is interfering. But I can take a measurement then take another right after and the results are very different... This is making no changes just doing another sweep.


I do not think it is a problem with the noise level, otherwise - you could increase the output volume. TDA test is generally rather sensitive to the position of measurement instrument (mic). It should be firmly mounted at the listening position. It is hard to achieve with the laptop in-built mic. I use omnidirectional mic Behringer 8000 - calibrated. Now I can produce almost the same results during TA tests. Apply averaging afterwords. It works for me.

But again - trust only your ears and you would be able to select the most suitable variant of time alignment for your system. 

Another question - internal sound card of a laptop. They used to be awfull. Mine (DELL) had deviations up to 8 dB. It is not acceptable at all for APL Workshop soft.


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## Alextaastrup (Apr 12, 2014)

crazhorse said:


> Im not sure but if I'm not loading the .fir files correctly or what but after measuring and using aplconfig to send the files to the unit before and after measurements are the same... unit has power, led indicators work and it is detected when I connect to it to load the files........


Strange. Something is wrong.

What about bypass? Is it off? Never experienced with such a problem. Please be sure you are using correct files. Check that you use the same channel (out of 16) for uploading and listening the results.

To check connection between the device and laptop (aplconfig) try to load "mute" for both fronts. Let say - to the channel "0". No sound shoud output if everything has been done correctly. The "mute" preset will be usefull in many cases in future (f. ex. tuning of subwoofer, ...).

During the upload procedure you have a possibility to check the window below of aplconfig. It shows current info: connected, done, etc. Very usefull.


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## Alextaastrup (Apr 12, 2014)

crazhorse said:


> Heres a sweep I took the other day of my system...
> 
> 
> 
> ...


If you are using mp1 as a target curve, it should not roll-off higher than 7 kHz. (Orange curve). Please check the limits under the test -6dB is not enough in your case. Could you send the inverted curve - EQ correction?

Again and again - omnidirectional mic with own (not generic) calibration file. It is critical.


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## crazhorse (Mar 9, 2010)

No I have the limits set for -18 low and high....... yes I have mp1 set as a target, its not showing to have cut the middle at all and to of boosted the high end



this is taking a measurement, which is the green line, applying the fir file for that measurement then taking another measurement which is the yellow line...
basically its not doing any sort of correction


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## crazhorse (Mar 9, 2010)

I mean all you should do is with aplconfig specify the left/right fir files for the measurement and then hit write to device correct ? If your not doing any correction in the way of peq... I havent been selecting a preset just sending the files to the apl1 ... is that the issue?


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## Alextaastrup (Apr 12, 2014)

It is OK to send separate files to the device.


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## Alextaastrup (Apr 12, 2014)

Beaming problems - how it was corrected in my previous install (tweeters in the front door triangles). Below are corrections separately for left and right tweeter.


















Correction was quite audible for 2-way system.


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## crazhorse (Mar 9, 2010)

Just sending the fir files to the apl1 not selecting a preset and its not looking like it does any sort of correction... Raimonds said bypassed is when just last 2 leds are lit and on is when leds show levels as music is played....... and its not bypassed when the measurements and corrections are applied..


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## crazhorse (Mar 9, 2010)

Alextaastrup said:


> Recently I have installed 3-way system in my car. It took less than one hour to test and tune it. Now I am enjoying music  instead of a nightmare of the time consuming tuning process. Really very powerfull device!
> 
> View attachment 92690
> 
> ...


Well its definitely not correcting my setup the way yours is in the second picture thats for sure... did you apply any peq to yours or just the correction curve ?


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## Alextaastrup (Apr 12, 2014)

crazhorse said:


> Just sending the fir files to the apl1 not selecting a preset and its not looking like it does any sort of correction... Raimonds said bypassed is when just last 2 leds are lit and on is when leds show levels as music is played....... and its not bypassed when the measurements and corrections are applied..


What exactly messages you've got in the big window beneath of the APL_Config?

It should be like: Device connected, writting to ..., done, etc. Or:

Operation failed. No device connected!
---
No active fast reload dir selected!
Operation failed. No device connected! if there is no connection to APL1.



Check actual current profile, which is channel number (down, right corner)
Check also the bottom line: Connected or Disconnected.

Check connection (another USB cable worth to try) and then reconnect the device (F1).

If measured curves and target curve are almost similar (as in your case above appr. 7 kHz, it will be difficult to hear the difference as a result of EQ correction. 

Please look once more time on these two pictures in my post #24. My tweeters also had roll-off, but after correction - they are very close to the target curve. Please notice the difference between this target curve and measurements (on the first graph). This difference should indicate the level of correction for specific frequencies. No difference - no correction, that is the point.

You should not make a new test. Is is possible to recalculate the results of the first test. Just change the limits (both up and down) to -18 dB and try to calculate one more time in order to receive new fir-files. Let me see results of recalculation. Number of recalculations is unlimited. This is a strong thing with this software. You could add f. ex. mic. calibration file as a correction, etc.

Do not forget that both the sound card and mic should be calibrated, otherwise good results could not be acvieved. Start with this first instead of changing the tweeters. Good luck!


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## crazhorse (Mar 9, 2010)

It shows to be connected and says the files are sent to the unit, and I get the progress bar showing the files being loaded. I believe it has the number 15 in the lower right hand corner.


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## crazhorse (Mar 9, 2010)

Alextaastrup said:


> Recently I have installed 3-way system in my car. It took less than one hour to test and tune it. Now I am enjoying music  instead of a nightmare of the time consuming tuning process. Really very powerfull device!
> 
> View attachment 92690
> 
> ...


Im not concerned with the tweeter roll off as much as it not correcting the low and midrange, the response thats above the target stays that way.
My system response is similiar to your first pic, your second pic which you said is the results of tuning shows alot of correction...
And if it is correcting by boosting on my measurments, it doesnt appear to be cutting frequencies that are above the target curve on my measurement after applying the fir files

From 100 to 180hz and 200 to 500hz or so on my measurement my systems response is above the target curve as well as 3000 to 5000hz so it doesnt look like its cutting those frequencies to match the curve.

In your pics it shows from 1k to 6k or so frequency response is above the target, in the second picture it matches the target curve so it has cut those frequencies to match the curve.
Like I said your second picture shows the freq response to line up with the curve, is that a actual measurement you took after applying the fir files ?


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## Alextaastrup (Apr 12, 2014)

Yes, my second picture is actualy two measurements (separately for right and left front channels), which I made just after aplying ther fir-files. No any additional equalisation/correction has been done for this. Just APL Workshop + APL_config. 

But this time I was lucky dew to better loudspeakers. Im my previous install, raw data (before APL) were rather poor (up til 17-20 dB deviation). I have experienced that in that case it was difficult for APL to solve the problem after only one run. I made 2 corrections more and the final picture became satisfying for me. Some modal problems in the car is generally hard to eliminate ...


Back to the business. Fine that APL_config can see the device and write to the channel 15. So far so good. Now you have to check once more what file are you trying to load: measured or the result of calculation. I have suggested to you to try to load the "mute" fir-file for both channels and to play it afterwords. APL should in this situation will cancell al the sound from both channels (left anfd right). Have you tried this? 

It is only to check how that APL is not defect and it understands the control comands. If this works, so we will try to look at your loaded file. But please make recalculations of the previous measurement aplying new limits. I used -18 dB and it worked for me.
Than - invert the target curve (at the bottom of the picture there is a knob for this. Then you could see the corrections to be done by APL1. Could you analyse them? How big corrections this time compared to the previos (made at -6dB limit)? Our ears can hear the difference more than 3 dB (ordinary people). Try this...


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## crazhorse (Mar 9, 2010)

Not sure on loading the mute preset, I see it listed in the c1 program in the preset box with a funny character as the first letter... in apl config it only has ones I have stumbled through making. I take it to create a preset you load the correction files for left/right channels in the boxes then hit the new preset option and it creates one with the 2 files selected correct?
As I mentioned only presets I have made show up in the apl config program not the mute flat no gain etc that show up in the c1 program.


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## Alextaastrup (Apr 12, 2014)

I have mentioned "mute" just as an option to see if APL1 works as it should. It should cancell the sound. Just to locate the error source. Until now it is not clear to me ...

There are various methods to load. You could load separate files for each channel: Mute_left and Mute_right, what ever. They should be in a relevant subdirectory.


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## Alextaastrup (Apr 12, 2014)

To load a preset form 3 different programs (Workshop, config and parametric eq C1) could be very tricky as you have to specify the same directory on your PC, which wil be shared between them. I preferer to load fir-files manualy and do make it easy - made a library for right and left-files.

In confiq you have to (as I remember) first browse your PC in order to find and select fir-files. Afterwords you could create and save new preset. Otherwise an empty preset will be saved.


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## Alextaastrup (Apr 12, 2014)

Are you sure you are loading the correct fir-file (obtained from Worshop calculations based on mp1 as a target curve? Curios to see the inverted orange curve (corrections).


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## crazhorse (Mar 9, 2010)

Ya using mic correction and mp1 as target.
Installing some 12mm spacers and adding more deadening to my doors today...


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## Alextaastrup (Apr 12, 2014)

Sounds good. Did you remember to try new limits and recalculate - just to see how it works after...


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## crazhorse (Mar 9, 2010)

The last set of fir files I applied took definite improvement in the sound. I haven't remeasured to see what it looks like yet. 
Only managed to get one of my doors done yesterday, got too dark to see. Will work on the other side today. I'll put up a picture of the inv correction from my last set of sweeps for you to take a look at.


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## crazhorse (Mar 9, 2010)

Heres the left side sweep from thursday, green being the power response yellow in the inv correction.







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this is with mic correction curve, mp1 target curve -18 on high and low frequency limiter..


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## crazhorse (Mar 9, 2010)

heres power response, target curve and inv correction








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it looks like the correction is more flat than what it should be correcting for the target...


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## Alextaastrup (Apr 12, 2014)

Something is wrong - I can not seen the inverted correction curve - difference between the raw data and the target curve. It should be also, orange colour as mp1 on your graph. This difference is a task for 4096 fir-filters to correct the sound of your system, leveling it directly to mp1.


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## Alextaastrup (Apr 12, 2014)

Some people underestimate importance of using the correct sound card for the tests in a car. I was one of them before I began to use t-Bone for my condenser mic.

First graph - measurements made with the help of in-built card.










The second - with t-Bone.









Finally - two graphs of looped cards (out-in):


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## crazhorse (Mar 9, 2010)

Well the second picture I posted is the right side measurement with power response correction and mp1 target curve all three are shown


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## crazhorse (Mar 9, 2010)

I'll try using my art usb preamp again and see if there's any major differences in the measurements.


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## crazhorse (Mar 9, 2010)

And which sound card are you using?

You mentioned calibrating your soundcard, do you create a txt file and load it as a curve for your soundcard like you do for the mic ?


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## Alextaastrup (Apr 12, 2014)

Well, my sound card with 48V for mic is almost excellent - you could see it on the graph. No correction would be needed. The most easy way is to make additional measurement with your card looped (out goes to in) with the help of APL Workshop and then use this new pr- or prs-file as correction to the actual measurement on the system.

Using Workshop - by checking "view as EQ" at the bottom of the graph, you will 
be able to see the difference that APL should make to original sound. It is practical tool.

My present sound card is t.bone MicPlug USB
the t.bone MicPlug USB - Thomann UK. Microfon - Behringer ECM8000


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## crazhorse (Mar 9, 2010)

I dont know, I played with a measurement not using a mic correction file, then calculating it with a mic file and the results are identical...
How does the program know the actual frequency response level without some form of cal file telling it other than increasing the volume when running a measurement?


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## Alextaastrup (Apr 12, 2014)

Mic calibration file is just an additional correction to your measurements. If you measure f.ex. high frequencies too high, this will be corrected during calculations. IT IS NOT NECESSARY TO MAKE MEASUREMENTS WITH THE MIC CORRECTION INCLUDED. You could do corrections afterwords. Without this calibration the Workshop takes the measurement results as they are.


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## Alextaastrup (Apr 12, 2014)

As can be seen - the tweeters and mids are places close to each other, so no time alignment required for them.

20150910_141735_zpsvlx0hjn5.jpg Photo by Alexander_Souproun | Photobucket


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## crazhorse (Mar 9, 2010)

I'm going to try another soundcard, I use my usb minidsp mic normally. I also have xlr mic and art usb pre which has xlr inputs but I dont care for it, so hopefully like you my problem is the built in sound because my measurements are wacky. After redoing my right door adding the spacer and adding some deadening took a measurement today and the right side response is worse than before....... and for some reason the low end just isnt being measured correctly for left and right, it shows to be way low when I run a sweep. And after running a sweep and applying the correction the sub is way too loud and boomy. Crazy stuff.
I got my apl1 without the preset switch, and the current profile on mine stays on 15. I dont know if thats because I dont have the switch to change between presets (other than choosing a different one with my laptop connected) and it stays on that one and over writes it each time I apply a fir. After emailing Raimonds about getting the switch I would have to solder on the socket to my apl1... nah dont want to do that so no switch for me.
Using the usb mic and the laptop soundcard output there isnt a way I know of to do a loopback correction, since input is coming through usb and out is coming from the laptop. I could do one with my art usb pre but I think my mic cable is defective awful pops for some reason. Why I went back to the usb mic...

todays sweep left/right
URL=http://s4.photobucket.com/user/crazhorse/media/right_01_1.jpg.html]







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With your tbone adapter are you running the headphone out to the apl1 input ?


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## Alextaastrup (Apr 12, 2014)

No. In my case it went directly to aux input of HU


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## crazhorse (Mar 9, 2010)

Did a loopback of my built in soundcard heres the result, suprised how flat it is...








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Maybe its the usb mic I have used for sweeps, or my laptop not having much memory.. had been planning on doubling the memory and upgrading the hd. Memory and a new hd should be here tomorrow.


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## Alextaastrup (Apr 12, 2014)

It surprised me as well...


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## Alextaastrup (Apr 12, 2014)

I wonder if I could hear a difference between processing at 24/48 (present APL1 hardware version) and a higher one (24/96,...). Theoretically I do understand that downsampling is destroying the sound, but 99% of time I listen music while driving. What experts are saying?


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