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Track device being used
The Equalizer
An equalizer is able to significantly improve the tonality of a car stereo system. The target of a properly adjusted EQ should be a smooth overall frequency response.
Features of the equalizer
1. The graphic 1/3 octave equalizer
All devices have 30 sliders in 1/3 octave steps between 25 Hz and 20 kHz for each individual channel. There are two exceptions, however: channels E to H of the PP 62DSP / PP 82DSP only have 15 controls in 2/3 octave steps between 25 Hz and 16 kHz. Each band of the equalizer allows a maximum boost of “+6 dB” and a maximum cut of “-15 dB”. This asymmetrical setting range was chosen on purpose, as boosts of more than “+6 dB” are very rarely required. Every strong, narrow-band dip measured in the frequency response usually results from a cancellation caused by a phase shift. An equalizer typically cannot compensate for this, or only very inadequately, even if greater boosts were possible. Experience shows that you should focus on eliminating peaks in the frequency response. The human hearing reacts much more sensitively to narrow-band peaks than to narrow-band dips.
3. The “Fine EQ” feature
Although the equalizer already comes with a very practical resolution in 1/3-octave steps, a “fine adjustment” for each band can be selected if a higher resolution is required. The “Fine EQ” function allows you to change the center frequency and the Q factor in small steps. To do this, click with your PC mouse on the desired EQ band, which is then highlighted in grey. The center frequency can now be increased by a maximum of 1/12 octave or lowered by a maximum of 1/6 octave in 1/24 octave steps. This means that it is not possible to overlap two adjacent EQ bands.Here’s an example:
The center frequency of the 1 kHz band can be raised up to 1,150 Hz. The adjacent “1.25 kHz” band can be lowered down to 1,175 Hz. It is therefore not possible to adjust two EQ bands to the same center frequency.
The “Q” control affects the bandwidth of a boost or cut. A small Q factor results in an effect on a wide frequency range, while a high Q factor allows to eliminate narrow-band flaws in the frequency response. The Q factor can be varied from 0.5 to 15 in 0.1 steps. The effect is shown in the graphic below.
4. The “Parametric EQ” function
The “Parametric EQ” function is similar to the “Fine EQ function”, but allows even more extensive setting options. Each EQ band can be switched to this function individually. As soon as you do this, the frequency is displayed in blue numbers instead of white underneath the respective slider. "Parametric EQ" allows you to change the center frequency in extremely fine 1 Hz steps - this is done using the up / down arrow keys on your keyboard. It is even possible to enter the frequency directly - just click on the numbers and type in the desired value. In contrast to the “Fine EQ”, there is no limit to the center frequency as long as you enter values between 10 Hz and 24,000 Hz for devices with 48 kHz sampling rate (or 10 Hz to 48,000 Hz for devices with 96 kHz sampling rate / 10 Hz to 96,000) Hz for devices with 192 kHz sampling rate).Important: Avoid having identical center frequencies for several bands if you like to boost a specific frequency range. The example shows what happens when four bands with the same center frequency are adjusted for maximum boost. Such settings almost automatically lead to digital clipping, which can destroy your speakers in seconds!
On the other hand, it is completely uncritical to choose the same center frequency for more than one filter if a certain frequency range needs to be lowered. This can e.g. may be necessary if one single EQ band is not sufficient to eliminate a peak in the frequency response.
This can be the case with narrow-band resonance problems of loudspeakers or vibrating door panels. Below you can see an extreme example in which four EQ bands were adjusted to 1 kHz center frequency with a Q factor of 15 and a cut of -15 dB each. The result is a -60 dB dip in frequency response.
5. The “Shelf EQ” function
The first EQ band (25 Hz) and the last EQ band (20 kHz) enable a further feature, the so-called “Shelf EQ” function. The first EQ band functions as a low shelf filter, whereas the last EQ band can be used as a high shelf filter. As soon as you have defined the lowest or highest EQ band as a shelf EQ, the frequency indicator underneath the respective slider is displayed in green colour instead of white. Shelf EQs are normally used when a wide frequency range in the low or high frequency range are to be boosted or lowered. Tone controls in car radios are usually designed as "shelf EQ's". The following is an example of a high-shelf filter with a corner frequency of 5,000 Hz, a Q factor of 0.5 and various gain settings:
The next graphic shows the same high-shelf filter, but here with a constant Q-factor of 0.5, -10 dB cut and different corner frequencies.
Below you can see the influence of various Q-factors with constant cut and corner frequency.
Warning: Always pay attention to the level bar for the respective channel when significantly boosting several bamds in the equalizer. The bar must never move into the red area, otherwise digital clipping and thus strong distortion will occur.
6. The “Allpass EQ” function
An all-pass is a filter that has no influence on the amplitude response of the respective channel, but only affects its phase response. The all-pass EQ is used to compensate for any phase differences between two channels. This can e.g. be necessary in a fully active system if the acoustic phase responses of the midrange and the tweeter do not perfectly match in the region of the crossover frequency range and thus resulting in a poor signal addition. An all-pass filter must not be confused with the delay function, even if an all-pass filter itself also causes a delay of the signal. However, the amount of delay is very much dependent on the frequency and the Q factor of the all-pass filter. With time alignment, any adjusted delay is frequency-independent.Here’s the typical amplitude and phase response of a first-order all-pass filter with a corner frequency of 1,000 Hz:
The graphic shows that the amplitude is constant over the entire frequency range, while the phase is shifted from 0 to -180 degrees. At the adjusted corner frequency, the phase shift is exactly -90°.
If you invert the all-pass filter, the phase shifts from 180 ° to 0 °, whereby the phase shift at the set corner frequency is then + 90 °:
On the other hand, if you choose a 2nd order all-pass filter, it creates a phase shift from 0 to -360 degrees. With the set corner frequency, the phase shift is exactly -180 °. Since the graph in the DSP PC-Tool can only show the range from -180 ° to + 180 °, the phase "flips over" precisely at this corner frequency.
The typical phase response of a 2nd order all-pass filter more clearly when it is inverted. Now the phase shifts from + 180 ° to -180 ° (here as well a total shift of 360 °), whereby the phase offset at the set corner frequency is then 0 °:
A 2nd order all-pass filter offers a second parameter, namely the Q factor. The higher you choose the Q factor, the narrower the frequency range will be in which the phase shifts by 360°. The following example shows a corner frequency of 1,000 Hz and a Q factor of only 0.3 and a correspondingly smooth phase transition:
The same all-pass filter behaves completely different with a Q factor of 3.0. The phase shift happens here rather abruptly in a narrow frequency range:
The maximum Q factor you can set depends on the selected corner frequency. All-pass filters with a high Q-factor tend to instabilities ("oscillations") and this tendency increases considerably as the corner frequency lowers. At 50 Hz corner frequency, the maximum Q factor is limited to 1.5, for example.
Important advice: Use the Q factor of an all-pass carefully. Values higher than 1.5 are rarely used. The human hearing is relatively insensitive to "gradual" phase shifts such as those produced by an all-pass with a Q factor of 0.3. If, on the other hand, large phase shifts occur in a narrow frequency range, the hearing reacts very sensitively.
7. The “Bypass” feature of the equalizer
For a quick sound comparison "with and without EQ", the equalizer can easily be deactivated. To do so, simply click the "BYP" button:
8. The “Reset” feature of the equalizer
If you want to set all sliders of a channel to the “0 dB” position, simply press the "RST" button:
To prevent this from happening accidentally, you also have to confirm your entry again in the pop-up screen:
9. Scaling the EG graph
For a better overview, it is possible to change the display areas of the EQ graph.
Vertical scaling
By default, a range from -25 dB to 10 dB is displayed. Clicking the vertical scaling button changes the range of the Y-axis to -35 dB to 20 dB.
Normal display view active, a click on this button switches to the extended display range
Extended display view active; a click on this button switches to normal display rangeHorizontal scaling
For devices with a higher sampling rate than 48 kHz, the scaling of the x-axis can be changed. This changes from a range of 25 Hz to 20 kHz to the view from 10 Hz up to half the sampling rate (“Nyquist frequency”) of the device.
Normal display view active, a click on this button switches to the extended display range
Extended display view active; a click on this button switches to normal display range
10. Selection of the graph display
For better visualization of cross-channel settings, it is possible to select in the menu to the right of the EQ graph which amplitude or phase curves of the individual channels should be displayed as an overlay.
If the “A” is shown in white, the display of the amplitude curve is active as long as the current channel is selected. However, if you want to display individual channels permanently, then simply click on the “A” or “P” of the respective channel.
If the “A” is shown in red, the display of the respective graph is permanently switched on.
In order to display all permanently displayed channels (red) as an electrical sum, the “A” at “Sum” must be activated.
Note: The y-axis is displayed logarithmically, which means that e.g. the sum of two signals, each with a level of 0 dB, adds up to +6 dB.
If “Allpass Control” has been activated in the DCM menu, the phase curve of the channel can be displayed permanently by clicking on the respective “P”.
The small loudspeaker symbol provides information on the current “mute status” of the respective channel. The icon can also be clicked to mute / unmute a channel.