DiyMobileAudio.com Car Stereo Forum banner

1 - 20 of 320 Posts

·
Registered
Joined
·
90 Posts
Discussion Starter #1 (Edited)
Introduction

First of all, I’m not a professional, just someone who used to be obsessive about mobile audio. So, please forgive any misuse of terms or definitions. Digital time alignment (abbreviated as TA) was the driving force behind my first active system. Based on recommendations by this forum, I put together a laptop-based measurement setup to help with setting time delays.

Long story short, I was never satisfied with the results. I put away the microphone and cables, and decided to use a different set of measuring devices: my ears. I experimented for weeks, and developed a way to set TA by listening for specific cues. The results were fantastic. The reason my method, with practice, will achieve better time alignment than any sophisticated measurement system is simple: it’s customized to every individual, and their vehicle interior.

With correct application, this method achieves immediate improvements in imaging, staging, impact, and transparency. Bass should become thinner, but in a good way - lean, with great impact. The sub-bass shouldn’t come from the back of the car, or even up front – it should be completely unlocalizable. Midbass should be solidly up front along with the rest of the center image.

TA will be calibrated:
  • Using your own ears
  • Taking into account your own hearing (the same sound is heard differently by everybody... and much more so by microphones)
  • With your head in your everyday driving/listening position
  • Taking into account all in-cabin reflections and absorptions, including your own body’s effects
The method costs nothing but time and patience. An audio file of pink and white noise will be used for tuning and can be downloaded free here: Burn-in wave files: white noise, pink noise, frequency sweep, channel mix

The method assumes that your system is an active one, with each channel individually adjustable for time delay. It is developed and written for a 2-way front stage with a mono subwoofer channel and no rear speakers, though it can adapted for any other active system, no matter how many channels. Note that there is only one sweet spot per calibration.

Here’s a preview of the method for a typical 3-way system:

While playing pink and/or white noise through system,
  1. Isolate sub and passenger side midbass (mute all other channels). Align drivers.
  2. Isolate sub and driver side midbass. Align drivers.
  3. Isolate driver and passenger midbasses. Verify time alignment and center image.
  4. Isolate passenger side midbass and tweeter. Align drivers.
  5. Isolate driver side midbass and tweeter. Align drivers.
  6. Isolate driver and passenger tweeters. Verify tweeter alignment and center image.
  7. Verify front stage alignment.
  8. Normal up the system and evaluate.
Notice that alignment takes place between 2 non-like drivers at a time (sub/mid, mid/tweeter), and verification is done using like drivers (both mids, or both tweeters).
 

·
Registered
Joined
·
90 Posts
Discussion Starter #2 (Edited)
The key to the process: what to listen for

The key to the entire process is listening for specific sounds which indicate when 2 given drivers are close to being in phase. Initially recognizing these sounds is difficult, but once you understand what to listen for, calibration will become easier and quicker. Here's a quick summary: 2 drivers play the same noise track and their outputs interact. Anything out-of-phase will cause harmonics. The harmonics will exhibit the Doppler Effect when time delay approaches the correct range. At the "center" of the Doppler Effect, harmonics disappear, which means out-of-phase information is at its minimum; the drivers are in phase.

Here it is in more detail. During tuning, pink and/or white noise will be playing loudly on 2 drivers at a time, and the noise will basically fill your interior.
  • The 2 seperate outputs will interact, and phase incoherencies will show up as subtle harmonics within the pink noise.
  • The harmonics will be at a much lower level than the 2 direct signals, and are difficult to detect. The goal is to identify and reduce these harmonics/phase problems to a minimum.
  • As time delay is adjusted, the harmonics will rise and fall in pitch. The changes in pitch will sound random at first, but repeatable patterns will appear.
  • As the drivers approach correct time alignment, the harmonics will exhibit the recognizable sound of the Doppler Effect.
  • The Doppler Effect will present itself in one of two ways, depending on which 2 drivers are being aligned, and their relative levels:
a) The pitch of the harmonics will increase, peak, and then decrease (Like the typical Doppler Effect) --OR--
b) The pitch of the harmonics will decrease, bottom out (the trough), and then increase again (Like an “inverse” Doppler Effect)​
  • In either case, when the Doppler Effect is at its extreme (the precise peak or trough), the harmonics/phase problems are at their lowest level, and the 2 drivers are in optimal phase.
  • Note: As delay is increased from 0ms upward, there are multiple occurrences of the Doppler Effect. The target is the FIRST one to present itself starting from zero delay.
Prep for tuning:

Save your current settings to memory. Since calibration will be done from your normal driving position, have your remote control handy, or make sure you can reach your controls while keeping your head steady and facing straight ahead. A battery charger would come in handy. TA is ideally set with the engine off, to make subtle sounds easier to hear. Make use of the charger (or drive the car) after tuning.

In your car, disable all filters/XOs external to your main DSP (stuff like on-amp filters, phase switches, bass controls, etc.). If you haven’t already, set your crossover points and slopes, and set your amp levels. Zero out all time delays and get your pink noise track ready to go, with the player set to repeat the track.
 

·
Registered
Joined
·
90 Posts
Discussion Starter #3 (Edited)
Tuning


1) Align sub and passenger side midbass

Mute all drivers except for these two. The sub will remain at 0 ms, and delay will be adjusted for the midbass. Begin your noise track (preferably pink noise since we're in the low frequency range) and turn up the volume loud enough to closely examine the signal.

Start increasing delay for the midbass, and listen to for changes in the sound. In the sub/midbass crossover region there are frequencies where both drivers are playing, and this overlap is out of phase. These harmonics appear as an incoherent rumble within the pink noise. As time delay reaches the correct range, the rumble will take on the pattern of the Doppler Effect.

More specifically, as delay is increased, listen for one of two possible occurrences:

a) The rumble shows itself around 60 Hz, rises in pitch to around 250 Hz, disappears, and then falls again from 250 Hz – 60 Hz.
b) The rumble shows itself around 250 Hz, falls in pitch to around 60 Hz, disappears, and then rises again from 60 – 250 Hz.

This event may occur anywhere between 0.75 and 3.00 ms. Try holding down the time delay key to scan quickly up and down between zero to 3.50 ms, this makes it easier to hear the pattern. When you think you hear it, note the approximate delay setting. Slowly scan up and down around that area and do your best to locate the center of the peak or trough, where the harmonics/rumbles disappear. This doesn’t have to be absolutely perfect yet, just get it close (the next step will fine tune the delay). Restore your normal XO settings and move on to step 1a.

(Note) If you’re having trouble hearing the Doppler Effect, go ahead and force both drivers to overlap and play the same frequencies – set both to play up to 300 Hz. Leave a 40 Hz high pass filter on the midbass to filter out low bass though. Go back and listen for the Doppler Effect again. When you’re finished with all of step 1, restore your normal XO settings and move on to step 1a.


1a) Verify your delay setting

The following is an example of how to zero in on, and verify the precise delay setting. Just as an example, say your best guess from step 1 is 2.00 ms delay.
  • Hit the delay “up” button and count how many presses it takes to hear a discernible change in phase (could be up to 30+, depending on time increments).
  • Say it takes 20 button presses to notice a change in phase (the rumble sound will return). Note the number 20.
  • Return to where you started – 2.00 ms.
  • Now, hit the down button the same number of times (20) – you should hear the very same rumble/phase change appear.
  • If it takes more or less than 20 presses, adjust your 2.00 ms delay up or down accordingly.
  • Repeat these steps until correct.
You’ve just eliminated the most apparent phase incoherencies between the 2 drivers, and they are now correctly aligned to your ears. And that’s how the method works. All other drivers repeat the same basic procedures. Each alignment depends on the one before it, so precision and patience in the first steps of the process is paramount.

(Note) This verification procedure will be repeated for all drivers.


2 and 2a) Alignment and verification: sub and driver side midbass

Mute all other drivers and adjusting delay for the driver side midbass. Note that because this midbass is closer to your ears than the passenger side, the time delay will end up slightly greater than the passenger midbass. The Doppler Effect will seem to appear and disappear more quickly as well.

Once you think you have the correct delay, verify using the same method as in (1a); this time, it should take fewer presses of the up/down button to hear a change in phase.


3) Verify alignment: both midbasses

Save your TA settings. You’ve just individually aligned your midbasses using the sub as their reference. Now it’s time to listen to both midbasses together. Mute all other drivers and return the XOs for the midbasses to their normal frequencies.

Play the pink noise and listen for the width and center of the presented soundstage. It should be quickly apparent that the image is solidly centered. If soundstage is not cohesive (almost like drivers are wired out-of-phase), or pulling to one side, then the best thing to do is go back to steps 1 and 2, and refine/re-verify your time delay settings. Making any arbitrary time adjustments during this verification step will do more harm than good.

An incoherent or off-centered soundstage can be caused by zeroing in on the wrong Doppler Effect (the second one that appears as opposed to the first one). As you get better at recognizing the Doppler Effect during the first 2 steps, the midbasses tend to automatically end up correctly aligned, and no changes need to be made in this step.

Don’t continue until you’re confident of your midbass time delay settings.


4 and 4a) Alignment and verification: passenger side midbass and tweeter

We’ll continue the process with the passenger mid/tweeter combo. Since this step deals with the midrange frequencies, playing back white noise instead of pink may be better (but not required). Use your normal XO settings, mute all other drivers and play the noise track.

The midbass will now be the reference; its predetermined delay setting will not change. Adjust tweeter delay until the Doppler Effect is heard. It will be more pronounced and easy to hear this time because the XO region is now in the midrange, and because the mid and tweeter radiating surfaces are physically quicker. The tweeter’s time delay should end up relatively close to that of the mid. If you have problems hearing the effect, use the XO filters to cut the high-end response of the tweeter, and cut the low frequencies of the midbass.

Verify using same procedure as above. It will take fewer button presses to hear a phase change.


5 and 5a) Alignment and verification: driver side midbass and tweeter

You know what to do. This one is a bit tricky because of the angle and proximity of the 2 drivers relative to your head. The Doppler Effect will come and go quickly. During verification, it should take very few presses of the up/down buttons to hear a change in phase.


6) Verify alignment: both tweeters

Save, or write down your TA settings. Restore both tweeters’ high-pass filters to their normal frequency. Listen to noise on both tweeters together and verify your settings from the last few steps. Again, listen for the width and center of the presented soundstage. Same deal, if it’s pulling to one side or incoherent, go back to steps 4 and 5 and refine/re-verify your time delay settings.


7) Verify alignment: front stage

Normal up the XOs for your entire front stage. Leave the sub off. Still playing the noise track, double-check for coherency and general staging. This is just a final verification of your settings, and if your verifications have been good up till now, this should not require any adjustments.


8) Normal up all settings and evaluate

This is the moment of truth. Normal up all of your XO settings, and save the configuration to memory. Play some music through your system and evaluate.

If you’ve never set TA by ear, and you’ve followed the steps with confidence in your determinations, there should be a very noticeable difference. Each time you go through the process, you’ll be better at recognizing the Doppler Effect and further refine your sound.

Improvements

With correct application, this method achieves immediate improvements in imaging, staging, impact, and transparency. Bass should become thinner, but in a good way - lean, with great impact. The sub-bass shouldn’t come from the back of the car, or even up front – it should be completely unlocalizable. Midbass should be solidly up front along with the rest of the center image.

That said, TA doesn’t magically transform your system into a rolling 5-digit audiophile’s dream. It just reduces the tendency for your speakers to fight against each other. Hearing correct TA for the first time can be downright shocking - but this is simply the moment we realize how much the speakers fight against each other within the confines of an automobile.

And, of course, this method is no replacement for a carefully installed system with well-placed drivers. But, it will definitely help a modest system with drop-in speakers bridge that gap somewhat.

Thanks for reading.
 

·
Registered
Joined
·
1,261 Posts
Will following this write up give you an image centered in front of the driver position or an image centered in the car?
 

·
Registered
Joined
·
12,571 Posts

·
Registered
Joined
·
90 Posts
Discussion Starter #7
Will following this write up give you an image centered in front of the driver position or an image centered in the car?
I'll assume "centered in the car" means along the car's center line, not "centered within the car."

Great question. The answer is a little bit of both, actually. If I had played a recording of a centered vocalist, I could point toward the image, and I'd end up pointing toward the front+center of the hood, where an emblem or hood ornament would be.

The method, by nature, forms a center image directly in front of the listener. However, this is pulled to the right slightly, because we sit on the left side of the car. It's the wide angle of the right speakers plus the low angle of the left ones.
 

·
Registered
Joined
·
90 Posts
Discussion Starter #8 (Edited)
I find this interesting, but if you are using the drivers with overlapping frequencies and then implement a crossover when you're done setting time alignment, wouldn't the resultant phase shift of the crossover change the relative driver alignment?

seems to me like you would have to set time alignment with all crossovers enabled, as the delay that comes with higher order crossovers will change the time alignment by the amount that each corresponding slope accounts for..

this is what I got out of the recent thread where lycan explains a linear phase shift, and time delay.

so, if you could find a way to implement the crossovers at their most tonally precise, then set time alignment with those settings in place you'd have a more exact positioning in acoustic space...

don't know if this is incorrect or not, just seems like the tutorial relies on setting drivers without the crossovers in play
Note that the overlap I suggest is between the sub/midbass only, by adjsuting frequency not slope. No overlap is suggested for the mid/tweeter.

This is another great question, I would have asked it myself! This occurred to me while developing my method, and after experimentation I've found that whether I overlapped or not, I still came up with virtually the same delay setting.

I experimented under these settings:
1) normal crossover settings (50 Hz LP sub / 60 Hz HP midbass 12dB/oct)
2) full overlapping (sub 0 - 250 Hz / midbass 40 - 250 Hz all 12db/oct)

These 2 extremes only led to a spread of +/- 2 steps (7mm/step, DRZ9255) with no discernible difference in sound either way - bass wavelengths are so long to begin with. At that point, I stopped worrying about phase shift in the bass region.

I don't have the knowledge to explain these results. All I can offer is that my method looks at phase in a different way. Everyone seems to looks at TA in the XO region through a microscope... Every dip or peak in phase response can be examined, and it makes you worry if any EQ or XO change will affect it. To pull out a worn out saying, too close to the tree to see the forest. My method takes a more simplistic approach. It blasts the entire XO region and beyond with energy, exposes the biggest phase problems, identifies and eliminates them. There ARE still phase problems present, but are very low in level. We want to cut off the heads of nails that are sticking out.

So far as my experimentation shows, calibrating with overlapping frequencies doesn't change the result significantly. I actually preferred to overlap because it was much easier to hear what I needed to, and therefore make a more definitive setting.
 

·
Registered
Joined
·
90 Posts
Discussion Starter #9
...and intelligibility is the rabbit in the crossover hat.
You making fun of my random cliché? J/K. Trying to understand your last post but not following you.

The biggest benefit of the method is in the midrange and how it aligns the tweeters to the midbasses. If you're still hung up on the overlapping thing, then don't worry - absolutely no overlap involved with the tweeter/mid. Intelligibility, height, texture, focus, impact - it will all be there. Because I can almost guarantee you've never heard your speakers work together like I will make them.

You've got an active system, right? Why don't you try the method, then I'll do my best to answer those questions that remain.
 

·
Registered
Joined
·
26 Posts
Ok I experimented with this technique some tonight. I could not hear anything in the "noise" when listening to the sub and midrange but I could when listening to the tweeter and midrange. Let me explain what I heard.

First my speakers are just in factory locations, 6 1/2 in the doors and 1" tweeters in the dash. My PRA-H400 delays in 0.3ms steps. I started with the passenger side mid and tweeter at 0 time delay. As I increased the tweeter time delay I could hear an "extra" sound that seemed to be coming from around the center of the dash. At 0.3ms it started, from 0.6ms to 0.9 ms, the sound persisted but changed in pitch. At 1.2ms the "extra" sound disappeared. So my questions are:

1. Am I listening to the right thing
2. Since the extra sound was not present at 0ms delay and appeared at 0.3ms and then disappeared at 1.2ms, was the first doppler effect at 0ms or 1.2ms?

Thanks!
 

·
Registered
Joined
·
90 Posts
Discussion Starter #11
Ok I experimented with this technique some tonight. I could not hear anything in the "noise" when listening to the sub and midrange but I could when listening to the tweeter and midrange. Let me explain what I heard.

First my speakers are just in factory locations, 6 1/2 in the doors and 1" tweeters in the dash. My PRA-H400 delays in 0.3ms steps. I started with the passenger side mid and tweeter at 0 time delay. As I increased the tweeter time delay I could hear an "extra" sound that seemed to be coming from around the center of the dash. At 0.3ms it started, from 0.6ms to 0.9 ms, the sound persisted but changed in pitch. At 1.2ms the "extra" sound disappeared. So my questions are:

1. Am I listening to the right thing
2. Since the extra sound was not present at 0ms delay and appeared at 0.3ms and then disappeared at 1.2ms, was the first doppler effect at 0ms or 1.2ms?

Thanks!
You've got the right idea, keep on it. I'll explain the mid/tweeter part first, since you are definitely hearing changes there. The same concepts can be applied to the sub/midbass part.

1) Yes, you are listening to the right thing. The "extra noises" you're hearing are the harmonics I described. It's out-of-phase garbage that we want to eliminate.

2) 1.2 ms sounds about right for a door mounted mid and dash mounted tweeter (it can't be zero ms because the tweeter is closer to you). Let's take a closer look at this.

From 0.3 ms to 1.2 ms, you noticed a change in pitch in the "extra noise." If you continue from 1.2 ms up to roughly 2.1 ms, you should hear the opposite change in pitch. Like I mentioned, you should hear ONE of these two things:

- pitch starts high, falls to low pitch, disappears, reappears as low pitch, then rises again
- OR, the opposite. pitch starts low, rises to high pitch, disappears, reappears as high pitch, then falls again

If you heard one of these, then yes, you successfully located the Doppler Effect and roughly found its center. Now, spend some time verifying that you have the true center (as outlined in step 1a of the method). Set tweeter to 1.2 ms. Step down to 0.9 ms then 0.6. Listen carefully for the pitch change that occurs. Go back to 1.2 and step up to 1.5 and 1.8 ms. The pitch change should be the same. If so, then you've successfully aligned the drivers. If the pitch change is not the same, then set the delay to, say, 1.5 ms and repeat until it is.

Now, for the sub/midbass. It works the same way, but the Doppler Effect is much harder to hear in the bass range. If you really have a hard time hearing it, then overlap the frequencies as described in step 1. Listen closely and you'll hear the same pitch change and disappearance of the "extra noise." Again, this noise will show up as a low rumble.

Don't give up on the sub/midbasses, the method can't be completed until you set this. After you do this, move on to the mid/tweeter alignment. Good luck, and come back if you have more questions.
 

·
Registered
Joined
·
90 Posts
Discussion Starter #12
Note: I had mistakenly listed time delay increments in centimeters instead of milliseconds in my write up. For example, I noted time delay as 70 ms, but I meant 70 cm (which is only about 2 ms). It has been corrected. Sorry if I made a confusing subject even more so.
 

·
Registered
Joined
·
4,014 Posts
Nice writeup here. I'll have to give it a shot. I usually just tune TA by playing a nice full range track and adjust the midbass to sub, then align the mid/tweet till i feel it's centered up.
 

·
Registered
Joined
·
90 Posts
Discussion Starter #14 (Edited)
Nice writeup here. I'll have to give it a shot. I usually just tune TA by playing a nice full range track and adjust the midbass to sub, then align the mid/tweet till i feel it's centered up.
You've got a real interesting install, nice job on that! I'm interested to hear your input regarding the time alignment, since your system is so far from typical. I like that you already time align by ear. My write up never accounted for an installation with the sub up front, only for the typical trunk-mounted installs. You probably already know how to adapt it for your car, but this is how I'd try going about it:

- Passenger midbass is the furthest low frequency driver, so this is the reference, and stays at zero delay.
- Align this with the sub, adjusting delay for the sub.
- Align sub and driver side midbass. Keep sub at determined delay from previous step, and add delay to the 5.25 until aligned.
- The rest of the write up applies from step 3 on, adding appropriate steps for a 3-way front stage.

Were you tempted to NOT time align the sub since you mounted it up front? Don't give in - definitely align them. It's the only way to bring out the synergy between the 3 of them. You'll get even more impact than the sum of the parts - and no matter where the sub is located, it will disappear, leaving all directional cues to the midbasses.
 

·
Registered
Joined
·
26 Posts
First let me say THANK YOU! I wish I would have had someone exlain this to me years ago. I have a CDA-7949 connected to a PRA-H400 via AiNet and an optical cable. My time alignment had been set by measuring the distance from each speaker to the driver's head and then set accordingly. I had made some minor corrections after listen to some music, mainly to the driver's side mid and tweeter to help center the image. The results were ok. Here are the time alignment values I had gotten that way:
Sub = 0
Driver's Mid = 5.4ms
Passenger Mid = 4.2ms
Driver's High = 5.7ms
Passenger High = 4.5ms

It wasn't easy to hear the sub/mid correction but after several hours, and finally raising the x-over on the sub I could here the "extra noise" and was able to eliminate or at least drastically reduce it.
After doing it the way descibed above my results were:
Sub = 0
Driver's Mid = 2.7ms
Passenger Mid = 1.5ms
Driver's High = 3.9ms
Passenger High = 2.7ms

The results are fantastic. The bass is leaner, tighter and not as "bloated" sounding. The highs are much smoother and blend perfectly with the mids. The imaging is centered perfectly and stays very tight and focused; before it wasn't real tight and it tended to wander some.

I am very pleased with the results.
 

·
Registered
Joined
·
90 Posts
Discussion Starter #17 (Edited)
First let me say THANK YOU! I wish I would have had someone exlain this to me years ago. I have a CDA-7949 connected to a PRA-H400 via AiNet and an optical cable. My time alignment had been set by measuring the distance from each speaker to the driver's head and then set accordingly. I had made some minor corrections after listen to some music, mainly to the driver's side mid and tweeter to help center the image. The results were ok. Here are the time alignment values I had gotten that way:
Sub = 0
Driver's Mid = 5.4ms
Passenger Mid = 4.2ms
Driver's High = 5.7ms
Passenger High = 4.5ms

It wasn't easy to hear the sub/mid correction but after several hours, and finally raising the x-over on the sub I could here the "extra noise" and was able to eliminate or at least drastically reduce it.
After doing it the way descibed above my results were:
Sub = 0
Driver's Mid = 2.7ms
Passenger Mid = 1.5ms
Driver's High = 3.9ms
Passenger High = 2.7ms

The results are fantastic. The bass is leaner, tighter and not as "bloated" sounding. The highs are much smoother and blend perfectly with the mids. The imaging is centered perfectly and stays very tight and focused; before it wasn't real tight and it tended to wander some.

I am very pleased with the results.
Enjoy your "new" system, thank you for commenting on the results. Isn't it eye-opening to find out how much potential can be unlocked? Now that you know what to listen for, running through the process in the future will be much quicker, and may refine your system even further.
 

·
Registered
Joined
·
90 Posts
Discussion Starter #18 (Edited)
got my system dismantled at the moment... trying out some wide-bander love before putting back horns..

what I'm saying is what you said, the midrange frequencies are going to be the more important considering how those frequencies functionally produce the panned monophonic that vocals require for that intelligibility, and any crossover in this region will be most affected by phase shifts in regards to how well vocals are reproduced. This is why I'd probably try and time align with crossovers engaged, including whatever protective caps are to be in circuit, just because you won't be able to correlate the final time delay to the doppler change if they are out of circuit. If you're using 24 db of slope, that amounts to 360 degrees at crossover, or one full cycle of delay, at 400 hz... well, you can do the math if you want...
My offer is simple; you put together the drivers, placement and XO settings for the kind of midrange you want and expect. Horns or widebanders, tune your system however you'd like. Then, follow my write up carefully, and see if you like it better. I'll personally apologize for your lost time if you don't like it. But, I won't apologize for the drool you get on your shirt after your jaw drops.

To calm your fears once again, any midrange or high frequency time alignment is completed with your crossovers at their normal settings. Overlapping or otherwise altering your sub/midbass XO won't change your results significantly - but can greatly assist with calibration. You're free to experiment of course, and come to your own conclusion.

BTW, you aren't by any chance testing out H-Audio's new widebanders are you? PM me about what you're testing and your findings, please
 

·
Registered
Joined
·
577 Posts
Greg, Thanks for following through from the other thread and posting the method. Very detailed. How small are the increments in your time alignment setup? Not that it really matters but some processors have .7cm while others have 2 inch increments. Just curious as the bigger incremental processors would more easily "blow over" the doppler effect if one does not really know what they are listening for in the tweeter transition.
 

·
Registered
Joined
·
90 Posts
Discussion Starter #20
Greg, Thanks for following through from the other thread and posting the method. Very detailed. How small are the increments in your time alignment setup? Not that it really matters but some processors have .7cm while others have 2 inch increments. Just curious as the bigger incremental processors would more easily "blow over" the doppler effect if one does not really know what they are listening for in the tweeter transition.
The write up was done with a DRZ9255 with 0.02 ms (0.7 cm/0.28 inch) steps. The average seems to be 0.1 ms steps (about 3.6 cm/1.4 inch), and the method has recently been successfully completed using 0.3 ms (about 10 cm/3.9 inch) steps. Even with the relatively large 0.3 ms steps, the Doppler Effect was reported to be around 7 steps "wide" in the midrange (in the bass region it's wider). Even if you might call this "limited precision," it made a big improvement. Smaller steps will allow a more precise phase alignment, but it's easy to see how it makes things more difficult:

0.30 ms steps (about 10.0 cm / 3.9 inch) --> approx 7 steps wide
0.10 ms steps (about 3.6 cm / 1.4 inch) --> could be 15+ steps wide
0.02 ms steps (about 0.7 cm / 0.28 inch) --> could be 60+ steps wide (!)

Which is why the write up is in such detail. DSPs with larger steps can still perform the calibration, and have an easier time doing so.
 
1 - 20 of 320 Posts
Top