Apple CarPlay has no bass

[Ben James]

I’m not sure if this has been mentioned in the forums already, but I was playing around with sub bass tone sweeps from my iPhone and discovered something interesting.

When I was doing bass sweeps wirelessly I had no problems going all the way down to 20hz which was playing through the subs as it should.

i decided to connect my iPhone so it was wired in (to use Apple CarPlay). When I went to do some bass sweeps I noticed that there was a massive bass roll off below 60hz.

I estimate that Apple CarPlay applies a 24db 50-60hz high pass which I verified with the frequency generator.

as soon as I disconnected from CarPlay and went back to a wireless (Bluetooth) connection the bass when back to a flat response.

For reference I’ve reset the response curve through Forscan so it’s hex is at 00 at address 727-01-02 (which means the APIM/ACM send out a dead flat EQ curve).

Just for info.

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[Snellemin]

Many moons ago, I had the same thing happen with my portable audio setup. I have quite a few high end headphones and being a basshead noticed this weird rolloff with the apple cables and other usb C cables. The rolloff came from the shielding used within those cables. My problem was solved with a "better" cable. You can produce this with shielded speaker wires and you will notice the loss in subbass.

 

[Ben James]

Weird… I’m using the OEM iPhone cable… I think I have another aftermarket cable laying around somewhere… I’ll change it over and see if there’s a difference.

 

[Mike Pfeifer]

Hm, interesting. I don’t have anything to add, but following due to interest. I have not checked wired vs BT, but would have assumed wired offered less compromises. Will have to try some things I guess.

 

[HoldenSSVandGT350]

Definitely interesting. I have a usb plug in wireless CarPlay adaptor so I guess I’m avoiding any strange high pass filtering in the 20-60Hz range because of it. My RF PW300 sub has the same output and extension as when it was in my SS Sedan.

 

[Ben James]

So… I went and bought a brand new aftermarket cable and thought I do some experimenting.

the bass rolls off in the exact place as the original cable, so I’m ruling it out as the cause.

It has to be the Apple CarPlay algorithm, which I have tested as having a 24db at 65hz high pass applied.

so… Apple CarPlay wired in has no bass…

This probably wouldn’t be noticed on OEM systems, but anyone with an aftermarket sub/amp combo would definitely notice.

 

[Mike Pfeifer]

Have you been able to confirm the same with different sources, like Apple Music, tidal, Plexamp, etc? How are you testing this?

 

[Mike Pfeifer]

I sent a message to a person I know that is both an audio guy, and an app developer that works with CarPlay. He has made his own audio software (filters and DSP stuff), so I bet he could be a big help here with looking into it.

 

[Ben James]

Have you been able to confirm the same with different sources, like Apple Music, tidal, Plexamp, etc? How are you testing this?

I tested it using a signal generator app. I listened to it wired through the usb when I noticed the lack in bass past 60-65hz, then when I went to wireless the bass response was all the way down past 20hz.

I first noticed a difference when I was listening to music on my Tidal app wired in to see if there was an SQ difference and I could ‘feel’ a lack in bass response compared to when I play it through a Bluetooth connection which is why I checked it with the frequency generator.

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