The iOS Application implements a smart low frequency room equalization technology.
auEQ presenting a frequency room response measurement
and the averaged target response
-------- Watch the Demo-Video to see auEQ in action --------
If you're using an iphone as music source for your HiFi-System then this app provides the next level of sound quality by applying a smart room frequency response equalization technology.
Your loudspeaker and amplifier combination may have a perfect frequency response within limits of +/- 1 dB over the whole frequency range but the listening room is the most critical component in the HiFi audio chain, causing amplitude peaks and dips of more than +/- 10 dB. Therefore, it is absolutely crucial to optimize the room by applying traditional acoustic measures and of course auEQ.
auEQ analyzes the low frequency magnitude response of the loudspeaker-room system and calculates the values of a full parametric set of equalizer-bands to tame the room resonances during playback.
The app consists of a room response frequency analyzer as well as a full gesture controlled equalizer and a customized audio player to reproduce the music through the calculated set of filters.
A smart equalizer just working on peaks in the low frequency spectrum by applying 64 bit precise filter algorithms ensures that there is no audible impact, but significant enhancement in music reproduction.
Controlling the low frequency (< 320 Hz) room modes leads to an improved bass reproduction and therefore a much better sound quality.
The following function blocks are part of the App:
1.) Low Frequency (20 Hz - 320 Hz) Room Response Analyzer
2.) Full parametric gesture controlled Equalizer
3.) Customized Audio Player
6 Easy Steps to achieve a better Sound:
1.) Place your iPhone at the listening position.
2.) Connect the iPhone via a cable (e.g. Headphone-Output) with you HiFi.
Music playback is possible via AirPlay too, but the measurement process needs a connection via cable or dock-connector!
3.) Start the 30 seconds measurement process by pressing the “Analyze” button. A slow sinus sweep excites the room modes. Make sure that there are no excessive disturbing noises during measurement.
Set the sound level in a way that there is no “Sound Level Warning” after the measurement has been executed.
The measurement result is shown by a white colored graph representing the room’s frequency response between 20 Hz and 320 Hz.
Furthermore, a green colored curve shows the target response for best correction.
4.) Set the equalizer bands either automatically, manually or use a mix of both methods:
a.) Press the “Auto” button for automatic EQ-Calculation.
The resulting filter curve is represented by a blue graph, whereas the estimated corrected room frequency response is shown by a red graph.
b.) Manual EQ-Setting by touch gestures:
- Select one of the seven EQ-Bands with the Stepper-Control-Element
- Set the filter frequency by swiping horizontally
- Set the filter attenuation by swiping vertically to control peaks in the frequency response
- Set the Filter quality (bandwidth) by applying a horizontal pinching gesture similar to zooming a picture
c.) The mixed approach can be achieved by first applying automatic calculation and then manual refinement of the equalization frequency curve.
d.) There is no need to achieve a flat frequency response. Just controlling the excessive peaks is crucial. The green colored target response helps in setting the filter parameter.
auEQ after automatic calculation and manual refining of
5.) Verify the Equalizer:
Similar to step 3 the analyzer generates a sinus sweep but now the equalizer is part of the audio reproduction chain to verify whether the predicted room response is similar to the real one.
An orange colored graph represents the measured room response after correction.
Lock the equalizer settings by activating the “Lock Switch”.
auEQ screenshot of the frequency room response verification showing that the orange verification curve
is nearly equal to the predicted red curve.
The 2nd screenshot shows the "Locked State" to avoid unintended changes.
6.) Use the auEQ internal audio player to playback music through your HiFi-System via dock-connector, cable or AirPlay.
auEQ internal audio player
auEQ in comparison to classical Equalization Techniques:
Most of the room equalization techniques work over the whole frequency range and try to correct for dips and peaks. This causes issues, which are described further down.
The auEQ limits its working range to frequencies below of 320 Hz that aren’t easy to control by classical acoustic measures like bass traps. Furthermore, by just reducing peaks, caused by room modes, the impact of the equalizer itself is very subtle.
Not touching higher frequencies does not mean that the correction is incomplete, in fact quite the opposite is true, because room modes of higher frequencies are very well controlled in a normal listening room filled with furniture and therefore do not create significant peaks in the frequency spectrum.
Technical details of the Analyzer, Equalizer and Audio-Player:
- The analyzer uses a slow sinus sweep to assure that all room resonances are excited to find significant room modes for equalizing.
- The equalizer works on peaks not dips to make sure that the non minimum-phase response of the room does not create problems like pre-ringing and phase errors. Room modes / resonances and therefore peaks exhibit a minimum phase response, which makes them an optimal target for the used IIR-filters.
- The filter algorithms of the audio core are implemented in 64 bit precision to ensure best audio quality.
- The full parametric IIR-filter algorithms are used in audio mastering applications too because of their musical sounding.
- Currently it is not possible to combine the smart equalizer with the iOS internal audio player, which made it necessary to implement a completely new customized player that offers an option to switch the equalizer ON and OFF for A/B-Comparisons. If there is an AirPlay device available then this can be selected for audio playback.
Frequently asked Questions:
1.) Do I need a special measuring microphone?
No, because there is no need to measure absolute values. We just need to identify peaks, which are then controlled by the attenuation of the calculated equalizer bands. An external microphone could improve the detection of very low frequencies, but the iPhone’s microphone is really good enough.
2.) Why not correcting dips in the frequency amplitude/magnitude response?
Dips do not contain much energy and would need a lot of gain and therefore amplifier power to be compensated. They exhibit a non-minimum phase response, which makes them difficult to control. Beyond that, dips in the frequency magnitude response are not that audible and therefore disturbing as peaks.
3.) Why don’t correcting the full frequency magnitude response?
Inverting the full bandwidth of frequency amplitude and phase response to try room response perfection causes several problems:
a.) The correction just works for a single very small listening position
b.) The wavelength of frequencies higher than 320 Hz gets quite short, which causes again problems with the listening position, whereas a correction of room modes applied by auEQ is nearly valid for the whole listening room.
c.) Artifacts like pre-ringing and phase errors get introduced. That is even worse for higher frequencies because it impacts the stereo sound stage.
d.) A complete flat room response causes an unnatural listening experience.
4.) How should I optimize my listening room?
It is always the best approach to apply first any acoustical measures possible. For example reduce the reverberation time for higher frequencies with normal furniture and for lower frequencies with special bass traps like Helmholtz-Resonators (if there is enough space). Unfortunately, those resonators are quite huge, which justifies the usage of auEQ to tame frequencies below 320 Hz.
Even if you’re not planning to use auEQ as audio player the app still provides a low frequency analyzer helping you to identify room resonances.