JetAudio graphic equalizer measurements
Jan 21, 2021
(Originally written in 2018)
JetAudio is a versatile media player for Windows and Android. It has a free (JetAudio Basic) and a paid version (JetAudio Plus) with some extra features (BBE effects, MP3 encoding). What makes the program really interesting is the built-in 20-band graphic equalizer. Sometimes we need the resolution of a 20-band EQ, for example, if we want to correct the frequency response of a mediocrate headphone or loudspeaker (without disassembling and changing the crossover or the speakers...). Other free players only offer a 10-band EQ and we have to install plug-ins to get more, but even JetAudio Basic on Windows has a 20-band equalizer almost from the beginning (since 2002, I suspect).
I measured the built-in graphic equalizer of the Windows version (JetAudio Basic 8.1.5.). Since version 6.0 the EQ has only been improved once in version 8.1.1. You can check the release history on the JetAudio website and decide if these measurements are valid for the latest version.
Pros of the EQ in JetAudio:
- Fine frequency resolution above 1 kHz.
- Good impulse response, no audible pre-ringing associated with linear phase FIR filters.
Cons of the EQ in JetAudio:
- Bad frequency resolution and separation below ~500 Hz.
- It's not possible to fine tune the bass below 100 Hz.
I never used the EQ presets (Rock, Jazz...). EQ presets named after a musical style are always useless. There is only one suitable correction EQ for every headphone or speaker, only the bass region where the setting depends on taste, style and loudness. For loudspeakers and for high SPL levels the target frequency response has to be as flat as possible (or at least this should be the starting point, e.g. Harman target curve has a small downward tilt). For low listening levels (background music) the bass region has to be boosted with some decibels.
I took some log-sweep measurements to test the performance of the equalizer. Below ~500 Hz the equalizer has low Q filters with large overlap, above ~1000 Hz the filters have high Q and very little overlap. In other words the EQ is very accurate above 1000 Hz and inaccurate below ~500 Hz. And we can't achieve the +-12 dB limits below 1 kHz (and hopefully we will not need it).
Here is an animation about how the equalizer works (setting each band one by one to "-12"):
And a table with center frequencies and maximum cut and boost per band:
The impulse response shows that the filters in the equalizer are so-called linear phase filters. The impulse response of linear phase filters have pre-ringing, and if the pre-ringing is too long it can be audible with transients. Fortunately, the pre-ringing in JetAudio is very short and cannot be heard with clicks and castanets even at the highest setting.
Linear phase filters have a very bad reputation as the impulse response of these filters have unnatural pre-ringing. However the audibility of the pre-ringing depends on the length of the impulse response (length of the filter). If the impulse response is shorter than 5 ms, then the pre-ringing can't be heard even with clicks (it will be masked by the impulse). It follows that below 500 Hz good frequency resolution and time behaviour can't be achieved with linear phase filters at the same time.
As we can see the range below 100 Hz where JetAudio EQ fails. Band 1 and band 2 seem to be shelving filters.
The X-BASS is a shelving filter with minimum-phase response. The bass boost is 5 dB with 50% and 10 dB with 100% setting. This kind of bass boost works well with small 3 or 4 inch fullrange drivers in a closed cabinet with bass roll-off at 150-200 Hz, but not suitable for large multi-way speakers or headphones. It would be a nice option to shift the corner frequency of this shelving filter somehow.