Table of Content
Introduction
The purpose of this article is to provide advanced guidelines to ensure better results from an ART calibration.
Before proceeding, it is assumed (and mandatory) that you’ve read the ART Guidelines and the other Application Notes from Dirac:
StormAudio x Dirac Live ART - Setup Guide
App. Note 1: Channel grouping and support settings
App. Note 2: Infra bass bypass
Based on this, you should already be well aware of the ART technology and the different settings available within the Dirac Live calibration tool.
Keep in mind that ART processing is a mathematical concept. Just as with a mathematical equation, if the tool is given bad information, you will therefore experience a bad result.
ART - In depth understanding
Reminder on what a Dirac Live ART calibration is made of:
Below 150Hz, Dirac-ART aims to correct the direct path of speakers and some of the room reflections with the help of other supporting speakers.
Above 150Hz, a “classic” Dirac-Live correction is applied to speakers.
ART is neither a cross-over technology nor any form of traditional bass management as you’re probably used to, it works differently.
The signal isn’t simply cut in two parts and spread between a speaker and the subwoofers as with Bass Control or a crossover. The signal is spread over the speakers and its supporting speakers to achieve a targeted direct path, phase, magnitude response and room reflections removal.
For any speaker, below 150hz, ART utilizes other speakers and/or subwoofers to support it and correct the speaker output.
Based on the defined target curve, this allows for additionnal degrees of liberty by creating:
a filter for the speaker on the full frequency range
a filter for each support speaker on the support frequency range
Supports frequency range
A crucial parameter to define is the frequency capacity range for each speaker.
First of all, you have to find the lowest frequency your speakers are able to reproduce. For a subwoofer, we also have to define the highest frequency it can reproduce in case it is lower than the 150Hz ART limit.
Setting this incorrectly can lead to a speaker overloading and possibly damaging it. Take special care to set this right.
You should not trust a Dirac Live tool measured sweep to characterize a speaker frequency range as room modes can influence the measurement and not reflect the actual frequency range of a speaker. By default, Dirac will not set a speaker supporting range below 50Hz, but this can already be pretty low for some speakers and should always be manually adjusted/checked.
A good rule of thumb is to trust the speakers datasheet for frequency range, often indicated as such (here is a subwoofer):
Frequency Response | 20 – 200 Hz +/- 3 dB |
Another but really more advanced way to check the frequency range of a speaker is to measure it, but from near field distance to take the room out of the equation. This can get really time extensive and not needed for most rooms but if you want to get as close to the real frequency response of your speaker it’s the way to go.
Once we have extracted this information for every speaker, here is what it should look like:
Speaker | -3db low frequency | high frequency |
|---|---|---|
L&R | 35 | -- |
C | 60 | - |
SUB 1 | 13 | 80 |
SUB 2 | 25 | 120 |
SUB 3 | 20 | 90 |
LS & RS | 80 | -- |
LFT & RFT | 120 | -- |
Table 1: Speaker Response based on datasheet
LFE management
Manage the LFE with care. The LFE signal goes to the main SUB (first in the list), and we have to define support for this sub. The other subs are the most appropriate channels for this task, and using only your other subs to support the LFE could be sufficient.
If your subwoofers are not able to reproduce some of the 20-150Hz, we recommend to add as support for LFE, if they’re capable enough:
The front scene (LF, CF, RF)
The back/rear speakers (LB, RB)
By experience, using only subs -and if needed the front scene- helps to get a more focused LFE with a good feeling of alignment. But in some difficult rooms, this may not be sufficient. In such cases, we encourage you to experiment and add other supporting speaker to help.
In our previous example, the three subs cannot reproduce frequencies above 120Hz. To ensure a good LFE reproduction, and provide ART more liberty to correct the LFE signal, we will add the L&R speakers as support:
SUB 1 supports | Low frequency support range | High frequency support range |
|---|---|---|
L&R | 35 | 150 |
SUB 1 | 13 | 80 |
SUB 2 | 25 | 120 |
SUB 3 | 20 | 90 |
Table 2: Subwoofers Focused Response Datasheet
You may note the overlapping frequency band coverage between L&R and the SUBs. In this example, between 35 and 120, L&R and SUB 2 are acting together as supports. It is better to have an overlapping support frequency range between speakers instead of relying on a single group to manage a support frequency range.
If we were to define a 120-150 support range for L&R because we think that it’s the only frequencies we need to be supported, we would likely get a bad bass optimization as ART will add Low and High Pass filters on the support filter at 120 and 150 Hz respectively. This would drastically constrain the correction we need in the sub-150Hz region.
Make sure to give enough liberty to the ART optimizer’s parameters to ensure a nice and smooth corrected response.
In any case, Dirac Live ART algorithm will then automatically take what’s best from all of your supports to ensure a good response for the supported channel.
Please also note that LR may not be sufficient to achieve a perfect result in your room between 120 and 150 Hz. In this case Ls&Rs could be considered to help as support. And so on with other speakers depending on the difficulty of the room.
While staying in the capable frequency range of your speakers, give the most latitudes you can to ART for it to work properly. Do not overconstray the support range and level, consider them as extreme limits, not what will be used in all cases.
ART - Supports settings
Here we’ll go in details on how to set the supports settings in the Dirac Live interface.
The first parameter to set is the ART support range. But in practice, you will first decide which group will act as support for a given group.
Grouping speakers
The Dirac Live tool gives the opportunity to set groups of speakers. A group shares, for all speakers in it:
a target curve
ART defined supporting groups to help this group
ART support settings to support other groups
Even if speakers share the above settings, they will have their own filters for ART support and Live correction based on the measurements, each speaker will be treated independently.
In our previous case, the three subs have really different response ranges. Therefore, it’s highly recommended to separate them into individual groups to set their support range frequencies properly.
Each different set of speakers (frequency capacity range wise) should have its own dedicated group.
Splitting speakers into more groups also allows for more granularity in the number of filters you can use in your ISP, but it also makes the configuration harder (more supports settings for each group).
Support range
The next phase will be to set the right supports range limits.
Each time you set a supporting group range for a speaker, make sure to match its frequency response range using the speakers datasheet. The table made earlier will help you quicken this task.
As previously mentioned, do not set a lower frequency range than the speaker is able to reproduce because this will lead to a very poor optimization from ART’s processing and eventually damage your speakers.
Overall, there is no reason not to let a capable support speaker act as support until 150Hz. This is why we set “--” in Table-1.
In the “Considerations” chapter, we will define special cases this setting could be fine tuned, but for most cases we recommend to let your speakers support up to 150Hz.
Support level
The last setting you want to modify is the Support Level.
Reduce the support level by increasing the value. -18dB is the default.
If you set it higher at -6dB: it will reduce the capacity for ART to use that group as support
If you set it lower at -24dB: it will increase the capacity for ART to use that group as support
As for Support Range, the Support Level is not a 1:1 operation, but rather a degree of liberty for ART, meaning that it may not always change the result of the calibration to the specified level, just set a maximum limit of use of a group for ART.
Considerations
Directivity
Directivity is the capacity to localize an audio source in space. Immersive content is based on this to immerse you into a movie/content, but for low frequencies, it works differently.
We know that for low frequencies, most people are not able to define a sound wave incoming direction. This is true as long as your room has some reverberation, absorption, scattering and as long as you are far enough from your speakers. This means that if your head is quite close to a speaker, you will be able to define where this signal is coming from, even for low frequencies. 80Hz sound from a speaker at only a few inches of a human ear will be felt as directive.
In ART, two parameters are then available for you to tune close speakers used as support:
Support Range:
Reduce the higher frequency support limit. The lower you set it, the less for human physiology to determine the direction of arrival will be.Support Level:
Reduce the support level by increasing the value. This constraint on the level of the support filter leads to less or more energy in the support speaker. By reducing the level, you will reduce the perception of the direction of the signal’s arrival.
Coherence
We know that audio systems are usually symmetrical. This statement could lead you to define left support with less constraint than the right support for a left speaker (reverse is also true of course).
To do that you will need to separate your left and right speakers in individual groups and differently configure each support group regarding its position. To sum up this simply, speakers close to each other can help each other with a higher level as this is coherent localization wise. But do not forget that mirror speakers at opposite sides of the room also have a really good position to manage reflections and correct each other (in regards to phase) . For example, both surround could be correcting themselves mutually.
SPL
Because energy is spread between speakers on their support frequency range, you will technically save SPL. This is true if speakers used as support have a homogeneous response in the support range. Then by tuning the support level, you will be able to spread the energy between your supports and in doing so remove excess load from the speaker to be corrected (this is often critical for the LFE).
However, most of the time this is not the case. Then the energy is spread through the speaker and its supports regarding their capacities in the room in term of magnitude and phase. This means that, if a speaker is the only one in the room to manage the frequency 53Hz for example, then all the energy regarding this frequency will be spread to this speaker. So you will, most of the time, end with an overall load that is split between your supports but with disparity. This will not ensure that your SPL is split between your subs for example. To overcome this issue and if you need more power in your room, you can physically group some subs to be considered as one speaker in the ISP. Physically, the power needed by each speaker will be divided by the number of speakers you group for a same SPL. The trade off you will face is the number of degrees of liberty in ART versus the maximum SPL you can manage with your speakers.
ART - Speaker settings
Front scene
In most cases, the front scene will need subwoofers to correct its lower frequency range. In addition to the subwoofers, we encourage to use speakers in the ear level to support the front scene low end reproduction as needed.
In any Home Cinema, the front scene is the most important set of speakers, meaning you should focus on correcting their frequency response first. They will benefit the most from being perfected as you will directly feel a new experience with ART.
The front scene is the second priority after the LFE to be considered for calibration and correction.
Center Speaker
In most Home Cinemas, the center speaker is quite critical. If you have enough speakers, we encourage you not to use the center as support for any speakers and use only sub and the front scene as support for the center. This will help to not overload a center speaker which have most of the time a very important signal to reproduce for the immersion.
Surround speakers
Every surround speaker should take the subs as support. This is a priority for low end response. Then you should add the ear level speakers as support because most of the time they are more capable than height or top speakers. Using the rules we defined earlier should provide a great response for each of these speakers.
Height and Top Speakers
Height and Top speakers can use any of the available speakers as support. You can try to focus using the front scene to help front heights and tops, and surrounds to help middles and back heights or top speakers.