Why milliseconds determine sound quality - practical tips for a harmonious sound image

Runtime correction in the car - what it does and how to set it correctly

If you want to achieve a perfect sound image in your car, there's one thing you can't avoid: delay correction. But what exactly does this mean and why is it so important for a realistic listening experience? In this article, we explain in simple and practical terms what delay correction is and how to set it correctly.

What is runtime correction?

In a typical car, the driver does not sit in the middle between the loudspeakers, but closer to the left side. This means that the sound from the left speakers reaches the ear earlier than that from the right. The human brain uses these minimal time differences to locate sound sources. If these travel times are not corrected, the sound image appears unbalanced or "pulled to the left".
Time alignment ensures that the sound from all speakers reaches the listener at the same time - in other words, that delays are built in to compensate for the natural asymmetry in the car.

Why is runtime correction important?

• Centers the sound image on the listener
• Improves staging
• Creates a more realistic, spatial sound
• Ensures harmonious interaction between all speakers

Without delay correction, music often sounds "out of place" or intangible. With it, it seems as if the singer is standing right in front of you. The instruments "stand" in their place and are clearly locatable, as if you could point your finger at them.

How do you set runtime correction correctly?

The goal is for all sound sources to reach the listening position at the same time. The ideal setting is for the driver’s seat. So, in your mind, push all the speakers away from you until they are all the same distance from your ear. You can think of this desired distance as an “orbit” along which the speakers are lined up.

There are several ways to set the optimal delay value. Below, we’ll explore two methods that make it especially easy for beginners to achieve good staging.

1. With correlated pink noise

All you need for this method is correlated pink noise and the ability to listen intently.

You can download the sound here:

Install the white noise on a USB drive or on your cell phone, and then connect your playback device to the radio or the Bluetooth module of the AXTON DSP. If you're using rear speakers and/or a subwoofer, turn them off temporarily.

The current value of the runtime correction (LZK) should be set to 0. Next, play the white noise through your sound system, keeping the volume at a modest, comfortable level. The louder the system plays, the harder it is to notice changes—especially when making fine adjustments.

The pink noise is playing, and you should perceive it vaguely—that is, it seems to surround you and is heard mainly on the left.

Now go to the LZK menu and gradually increase the delay value for the left speaker. Pay close attention to what happens as you do this—how the noise changes. You might even want to close your eyes to help you concentrate better.

Once you reach a certain value (which varies from vehicle to vehicle depending on the model), you should notice how the diffuse pink noise gradually forms a sort of “cloud” that focuses on a very small area directly in front of you, or centered on the dashboard. As soon as you notice the cloud expanding again, reduce the delay slightly. Keep trying until you see the most compact cloud. If the cloud is perfectly formed but isn’t centered, adjust the level on the left or right side until the cloud hovers in the desired position.

Next, you'll take a hearing test using a professionally recorded song. We recommend the following songs:

• Adele's voice in "Hello," for example, is recorded perfectly centered.
• "Young Folks" by Peter Bjorn and John: The male singer is slightly to the right of center, and the female singer is slightly to the left of center
• In Michael Jackson’s classic song “Thriller” (from the HIStory album), a man runs from right to left. In the car, his steps should look “natural” and believable. If the man suddenly stops in his tracks—especially on the left side—the camera angles will need to be fine-tuned again.

Note:

For a perfectly compact soundstage, the individual components of the front system—that is, the tweeter and woofer—must play in sync with one another. In passive systems where the distance from the speaker to the listener varies, time alignment correction is not possible. So you have to accept that, while the soundstage is compact, it may not yet be perfect.

The rear speakers are adjusted using the same method. The sound should be aligned along the same axis as the front system. So if the sound “cloud” hovers directly in front of you with the front system, it should also be positioned directly behind you with the rear system. Once the rear system is set up, the final step is to synchronize the front and rear systems in terms of timing. To do this, we’ll activate both the front and rear systems and delay the entire rear system until we perceive the “cloud” as a compact shape on the dashboard again. Please make sure that the difference between the left and right rear speakers remains unchanged.

The rear system is perfectly integrated if, when you turn off the rear speakers, you don’t notice the soundstage shifting to the right or left. The perceived sense of depth should also remain unchanged. If the music sounds flat, check the settings for the rear speakers again. Depending on the vehicle, reversing the polarity of both rear speakers can also create an extremely deep soundstage.

2. Using a measuring tape

The tape measure method is generally best suited when you're only powering a front speaker system. Due to reflections inside the vehicle, the measured values for the rear speakers may differ significantly from the actual distance. The tape measure therefore provides only rough estimates, which you'll need to fine-tune through careful listening.

1. measure speaker distances

To begin with, we measure the distance from each speaker to the driver's ear. The best way to do this is to use a tape measure or folding rule from the speaker to the headrest.

Now determine which speaker is the farthest away—it defines the reference plane—and subtract the distances of the remaining speakers from that distance. Then enter the difference for the respective channel in the AXTON DSP so that they also end up on this path. Example: The subwoofer is the farthest away, at a distance of 2 m from your ear, while the front left speaker is 0.80 m away. Then note down the difference of 1.20 m—that is, the required delay—for the front left channel. The front right speaker is 1.30 m away from your ear; therefore, the delay value would be 0.70 m for the front right channel. 

2. convert distance into milliseconds (if necessary)

A rule of thumb: sound requires approx. 0.029 ms per cm. Example: If the right speaker is 30 cm further away than the left speaker, the left speaker will have a delay of approx. 0.87 ms.

3. enter distances into the DSP or radio

Our AXTON DSPs (digital sound processors) A544DSP, A594DSP or A894DSP offer you the option of entering the runtime for each channel in centimeters or milliseconds.

4. fine-tuning with test music

Use well-produced pieces of music or test tracks to fine-tune the running times. Voices should come clearly from the center, usually somewhere between the rear-view mirror and the steering wheel, and should not "wander". So if the singer seems to have a mouth two meters wide, check your settings again.

5. Note on Subwoofer Settings

The procedure described above generally works very well when setting up the front speakers. However, for the subwoofer (or the rear door speakers), the measured direct distance between your ear and the speaker may differ from the actual optimal value for time alignment. The reason for this is that low frequencies do not propagate as a narrowly focused sound beam but instead excite the room over a wide area. In addition, reflections from the subwoofer (or the rear door speakers) can affect the effective time delay.

So feel free to experiment with values that differ slightly from your measured distance. The less the subwoofer stands out from the overall sound and the harder it is to pinpoint its location, the better the setting usually is. Be careful not to set the subwoofer too loud, though, because otherwise it will sound dominant regardless of the time alignment correction and will be easier to locate.

Conclusion

Time alignment is an essential tool for getting the most out of your car hi-fi system. It corrects acoustic imbalances caused by the asymmetrical seating position and ensures a realistic, centered sound image. With a little patience and sensitivity, you can achieve an impressive difference.