The Audison AF Forza bit amplifiers are advanced DSP sound processors. Using DSP processing to get great sound can be a little overwhelming. We are often asked where to start. Well, there is more than one way to arrive at a great-sounding car audio system using DSP - but here is a proven tuning process which delivers great stereo sound for the driver’s seat in a reasonable amount of time. Before we start, here are a few things you need: A source of mono-pink noise. The downloadable tracks for AF Forza contain mono-pink noise. Many head units lack a “repeat” function, so it can be very convenient to have a USB drive or CD with just this one pink noise track and no other test tones. A USB measurement microphone. You can also use an XLR measurement microphone and a USB sound card. We recommend using two active USB extension cables - one from the USB microphone to the laptop, and the other from the PC to the AF Forza bit amplifier. Finally, it’s best if you can connect the vehicle to a clean source of 12 volts DC, so the battery does not deplete before we are finished. In this basic example, we are using a 2-way active front stage, and a subwoofer. For simplicity, we are not discussing any advanced systems. We will address more complex systems in future videos. When you’re ready to tune your auto sound system, you will have already completed the first steps in our AF Forza video tutorials. You’ve installed the software and firmware. You’ve initially configured the bit Drive software. You’ve used the configuration wizard to define and set up the system And, if you’re using an OEM source for signal, you’ve used our de-Phase process. If you’ve done all that, you’re ready to tune the system! Step One - Confirm that your input signal is flat and full range. To do this, make sure all the tone are centered or set to “0”. Turn the volume of the system off, and play mono pink noise at about 75% volume on the OEM head unit. Click on “Inputs” in the bit Drive software. Then click on the “Input EQ” icon here. To View channel one, click on “1” here. You should see a flat, full-range signal like this. Click on Channel 1 again to de-select it, and then click on Channel 2 to view Channel 2. If it also looks flat and full-range, click on “1” again to sum the two together and view the result. If one or two large dips appear, the signal has been phase processed with all-pass filters. DO NOT proceed to tune the system until you’ve corrected for this! Refer to Episode 4 of our video tutorials. If a series of dips appear - a “comb filter” - the signals are delayed in the time domain relative to each other. Do not proceed to tune the system until you’ve corrected for this! If the signal simply goes up in level 6dB, then the signals are aligned in phase and time, and you are ready to tune. Step Two - Enter your crossover points and your speaker distances. The bit Drive software will enter basic crossover points for each speaker, to reduce the risk of speaker damage. For best performance in a given system, different speakers can benefit from specific crossover settings. Audison has published a list of recommended crossover settings for our various speaker systems. This link here shows us that the cabin crossover points are all linked together. I’ll show you what that means in a moment. Click here to change from the System Map to the System List. Here you can see all the crossover settings at one time. Since many target curves set the subwoofer at a higher level than the midrange, getting the crossovers to sum flat in this region can be a problem. Many system tuners use the “one-half octave gap” technique. If the front speakers have an 80 Hz high-pass frequency, one-half octave below that is 60 Hz. We’ll cover this in more detail another time, but for now, we will set the subwoofer to 60 Hz. Now we go to the tweeter. The default setting for the tweeter is 5000 Hz - but Audison tweeters can play well below this frequency. For this system, let’s use 3200 Hz. Click in the text field, and type in “3 - 2 - 0 - 0”. You can see that the opposite-side tweeter is now populated with the same value - and the midranges are now low-passed with the same value. The default setting for bit Drive software is the metric system. If you want to change it to the Imperial system of measurement, you need to do that in the system Settings in the software. Now we will enter the distances to the speakers. If you haven’t measured the distances to the speakers already, you will want to do that with a tape measure. Measure from the driver’s headrest to each speaker, and add in the distance that you think the speaker is behind the grille. Now that we’ve entered in the distances to the speakers, you can see that the software has calculated the delays required to put the speakers back in phase with the farthest speaker. In this case the farthest speaker is the subwoofer, and you can see that no delay has been assigned to the subwoofer channel. Step Three: Quality Control. Now that we’ve set our crossover points, let’s do a quick quality control check. While this part seems easy to pass over, an error here can waste a great deal of time trying to tune an untunable system. You should still be playing mono pink noise. Turn up the volume of the system here, until you can hear the pink noise from outside the vehicle. Open the door of the vehicle. Now, using the “Solo” buttons here, play each speaker one at a time, and confirm that the correct speaker is playing in the cabin. If you have a polarity tester, this is the right time to use it. If any speakers are connected improperly, you’ll need to correct this before you go any farther. Step Four: Set up the bit Drive audio analyzer. First, let’s set up the microphone. In this example, we’re using a Mini DSP UMIK 1. Install the mic and mic holder onto the stand if you’re using a stand Connect the included USB cable to the microphone Connect the other end of the USB cable to your USB extension And connect that to your PC. Place the stand in the driver’s seat, approximately at the listening position. Now, let’s set up the RTA. Click on “Audio Settings” here. Select the USB microphone that you’re using. In this example, we have an external USB sound card displayed, and the PC internal microphone displayed. Make sure you don’t select the internal microphone. Select the resolution for the RTA. While it can be tempting to select the highest resolution available, we recommend - until you’re experienced at acoustic tuning - use 1/3rd octave resolution. You can also select the refresh rate. We recommend “Normal” for acoustic tuning. Now, turn on the RTA with the Microphone icon, here. You should see something like this on the graph. If you’re not seeing anything on the graph, you have to sort that out before you go any farther! Adjust the high and low boundaries of the RTA graph using these settings here. You want to get the response fairly centered, with about 30 or 40dB between the top and the bottom. You don’t want the graph over-compressed vertically, or stretched too much vertically. Now let’s set up our target reference curve. Mute all speakers except the far front mid woofer. To do this, you can use the Solo function, or you can use the Mute buttons. I’m going to use the Mute buttons in this example. Select the far front mid woofer to equalize. That channel will be highlighted on the system map, and the user interface will use the same accent color for all the controls when you’ve selected this channel. Click on the Reference Curve Icon here, and select a target reference curve file. I like the E curve. Now, we have a decision to make. Once we set the level of the reference curve, this becomes the reference for the entire system. Do we position this curve high, so that dips will have to be boosted to reach the reference level? Or do we set it low, so that the peaks have to be attenuated to reach the reference level? This decision is usually made on a case-by-case basis. Not all dips can always be boosted sufficiently to reach the reference level. Since +3dB of boost requires double the power at that frequency, it is easy to run out of clean undistorted power if we use a lot of gain here. As a rule, setting the reference curve at the bottom of the dip results in a better-sounding system with less chance of distortion - but it also often results in a system which won’t play quite as loudly - especially if you’re starting with lower-powered amplifiers. In this example, we’re going to set the reference curve here. Step Five: Adjusting the EQ - starting with the far front side. It’s possible to tune a car using the Graphic EQ mode - but it’s a much less powerful tool. We’re going to use the default Parametric Equalizer mode. Identify a peak. Use the cursor to click at the top and center of the peak on the graph. That will show you the frequency of the peak and the dB level of the peak on the graph. Here, this wide peak is centered around 180 Hz. Select an EQ band. This band is already set pretty close to the frequency we need - 160 Hz. Click on this slider, and either drag the slider down, or use the Down arrow key on your keyboard, to pull energy out at that frequency until we reach the target reference level. There - we’ve addressed a lot of that big peak. Now we will select another EQ band - this one is also already set to the proper frequency and we will pull energy out of that frequency until it reaches the target curve. This peak is at 250 Hz. There is already an EQ band set to that frequency, Now that we’ve pulled to adjacent sliders this far down, it looks like we are a little bit lower than the target reference. Let’s adjust these back up a bit, and see if we can get back to the level of our reference curve. Now let’s look at this peak on the right. We don’t have an EQ band already set to 2000 Hz - so select an EQ band, then click on this text field to enter in the frequency we need. Then we click on the slider and pull it down until we reach our target at 2000 Hz. OK, the last peak is around 1000 Hz. We already have a slider positioned there, so pull that one down. There does seem to be a slight dip at 500 - let’s select an EQ band, place it at 500 Hz, and nudge it up just a bit. Now let’s click here, just to get this trace out of the way, and compare our result to the target curve. You can see we’ve followed the reference pretty well. Now let’s mute the far mid woofer and play the far tweeter. It’s pretty common for tweeters to be much louder than the reference curve, and need to be turned down. Depending on the response, we may use the level control for this, or the Equalizer, or a combination of the two. Click on this slider, and pull some energy out of this output channel, getting the result closer to our target. This peak here is around 9000 Hz. Let’s try our 10k slider. That’s pretty close. Now let’s use the 16k slider and pull energy out from there. Wow - that’s right on target! Now let’s play the far midrange and the far tweeter at the same time. Pay special attention to the transition band here. If you see dips appear at the crossover region when both speakers are played, that indicates a phase cancellation where the speakers are overlapping. In this example, that crossover region looks fine. We’re doing a good job of matching our target reference curve. Now, lets turn on the subwoofer. We have a lot of sub bass! Probably too much. We also have a bad phase cancellation right here. This damages the midbass response, and it also will ruin the “bass up front” effect we are usually trying to achieve. So first, let’s reverse polarity to our sub channel so see if this cancellation disappears. Wow! That really took care of that! Now let’s adjust the subwoofer level and EQ. We need to know at this point if the system has a subwoofer level control available to the user. It might be inside the head unit, it might be a feature of an interface device, it might be our DRC controller for the AF Forza, or it might be that the subwoofer amplifier has its own level control. Whenever the system has its own level control, we recommend you turn down the subwoofer level using it - roughly 6dB. That way, the user can ask for more sub bass than the reference level, when desired. Even with 6dB taken out here, we still have too much sub bass content. There’s also a peak here at 60 Hz. There is already an EQ band set to 63, so let’s use that band to pull out some energy. OK, that’s still more sub-bass than we need, but it’s pretty close to our target, and the user can adjust the sub-bass as desired. Now it’s time to make the near curve match the far curve. Mute everything but the near mid woofer. Wow. We’ve got too much energy from that speaker - so let’s pull that down. There’s a big peak at 1k. We already have an EQ band there, so let’s pull that down. We still have a lot of energy. Let’s select a band near the center of this really broad peak, and change the bandwidth here to a wider value. 0.5 here will widen the number of frequencies affected by a single slider. Let’s pull that down. OK, that helped a lot. You can see we have too much energy at 1600 Hz, let’s take some out there. OK, that’s pretty good. Now let’s address this 250 Hz dip. Now let’s put a band at 500 and widen it out. OK, we’re following our target pretty well. Now, let’s mute our near mid, and play our near tweeter. Again, there’s that big peak. Let’s pull some energy out of that at 10k and 16k. Now let’s take some energy out of the entire channel, here. Oh, that’s really close to our target Now let’s play the near midwoofer and the near tweeter at the same time,. That’s pretty good. We did lose a few dB at 4K, let’s see if we can EQ that back to our reference target. Hey, we did! Step Six. Now let’s play the front speakers and the sub - which in our example is the entire system. You can see we’re around 6dB louder than the reference target almost everywhere. In the treble, we’re only about 3dB louder, which is to be expected - and there is a cancellation at 250 Hz, pretty clearly. Now, let’s just try an all-pass filter at 250 Hz on one midrange. It may or may not work, but it’s easy to test. Pick an EQ band, and select “2nd order All Pass Filter” at 250 Hz. OK, that worked like a charm - now we’ll see how it sounds when we listen to it in a few minutes. Let’s use the Final EQ to smooth out the treble. The Final EQ affects all channels at the same time. OK, we have followed our Reference Curve pretty well. No speaker system is perfect, but this is measuring really well. If we have the time, we can work on some of the small areas of deviation - but this is entirely optional, and depends on the situation that you’re in. D Step Seven - it’s time to test the stereo imaging. Many tuners use test tones intended to appear at specific locations in a stereo system - or at specific frequencies - to test the imaging. Some listen to specific songs The test tone technique is the fastest and most efficient. If any tones intended for the center of the vehicle appear to be off-center, that means the left and the right sides are not matched in level at that frequency. If any test tones intended for the center of the vehicle appear to be split to the sides, that indicates there’s a phase problem at that frequency Step Eight - Listen to Music To make any adjustments to the sound of the system, use the Final Tune EQ, so that all the channels are equally affected, and your imaging isn’t damaged. When the entire system sounds great, finally - it’s time to finalize! Step Nine. This makes sure the settings are saved to the nonvolatile memory inside the AF Forza amplifier. It’s also a good idea to save this file to your PC desktop with a filename telling you which car it was used in. OK, that was a few steps - let’s review them again! Step One - confirm that your signals are linear in phase and time Step Two - Enter your crossover points and your speaker distances. Step Three - Do a quick quality-control check. Step Four - Set up your audio analyzer Step Five - Adjust the Equalizer, starting with the far front side Step Six - Measure the entire speaker system, and adjust it Step Seven - Use test tones to confirm the imaging is where it should be. Step Eight - Listen to Music Step Nine - Save the file and Finalize it to your AF Forza That’s it! We hope this video has taken some of the mystery out of tuning a DSP amplifier, and helps you get great sound from systems that use AF Forza. Thanks for watching! [Music]