It sounds like your suggesting that Toyota purposely placed an all pass filter in their radios? That would be hard to believe. Your measuring an acoustic issue that is a product of the environment. I would guess that your measuring for comb filters in relationship to the vehicle node which is causing an imperfect cancellation. The only way to truly know is with an FFT measurement system. An all pass filter is an electronic filter set that changes the phase of a defined pass band without affecting the frequency response. A first order filter changes the pass band by 90 degrees and a second order by 180 degrees. Pink Noise is all frequencies, but not all amplitude. It has an applied EQ curve that best represents human hearing. There is more weighting applied to the lower frequencies. White Noise is equal amplitude applied to all frequencies and shouldn’t be used to optimize your sound system. The display on the iPad prior to measurement is commonly referred to as the noise floor of the measurement rig. Higher quality measurement systems such as Smaart, won’t show you the noise floor unless you alter dB scale because the noise floor so low. I got out of 12v audio 26 years ago to become a system engineer for large concerts. I use electronic all pass filters to manipulate the phase as part of my daily routine. 26 years ago the SNI35 was one of the most used adapters then when I was an MECP installer. Glad to see that that no one has ruined a perfect product and you no longer have to mount the that old Honda radio behind the new aftermarket radio to maintain control keyless entry. 😀
