@Tideland Prius might be able to help you out with this, but I can't sorry. Welcome to Prius Chat and wait awhile till someone tells you the answer.
Is this what you're looking for? If you're talking about audio codecs, this is for MP3 CD This is for USB or iPod devices
Thank you for all of this detail. I am asking specifically about the implementation of the A2DP. I cannot post links, but please search for A2DP in wikipedia. From this article, you can see that A2DP is the profile within bluetooth that plays audio over bluetooth. Audio sent over the limited bandwidth of Bluetooth must be compressed via a codec. All A2DP units must support the SBC codec, which is generally panned by those that are looking for good sound. aptx is an optional, but increasingly supported, codec within A2DP. So, since this head unit supports A2DP, we know it must support the SBC codec. The question is: does it also support the aptx codec?
Since the manual does not state it, I would expect they do not support the optional codecs. To know for sure somebody with the proper audio player would need to test. If you have such a player, perhaps you could try it at a dealer.
This is an old thread, but I couldn't find any newer information. I have a Pixel 4 XL and a 2018 Prime Plus (base model). I turned on debugging on my phone, and I saw that the SBC codec was selected, but AAC, AptX, and LDAC were grayed out. Presumably that means the car does not support them. I will try forcing it to a higher sampling rate (48 or 96 kHz instead of 44.1 kHz) or a higher but depth (24 instead of 16), but I don't have high hopes for that working at all, let alone improving quality.
Aha, does that answer the question of sound quality difference for BlueTooth vs USB direct connection on PP? I have no idea what sampling rate the USB connection is using, but if it is always higher than what BlueTooth is using, then it sure proves that USB sounds better.
I have an Android phone, and I couldn't figure out how to make USB direct connection work. It was grayed out on the car. Is it an iPhone only thing? Bluetooth uses lossy codecs, and SBC is not optimized for maximum sound quality. I don't know what USB uses, but I assume it's better. If it's lossless or that same native compressed format as the source, then it's potentially even better than an aux cable if the DAC in the head unit is decent. It seems to be easy enough to make a decent DAC for pennies, but then again I wouldn't be surprised if Toyota found some kind of dinosaur solution that's more expensive and lower quality.
Based on Tideland's post above, it sounds like USB probably transfers the file natively from the USB device and decodes in in the head unit. That will almost always be better than bluetooth which recompresses audio. And it depends whether that's better than an aux cable, but it could be if the head unit is designed well.
I found some info about USB in an old reddit post. Code: https://www.reddit.com/r/GooglePixel/comments/5namj8/comment/dcaeois Ironic that the device that goes to great lengths to hide the file system uses USB mass storage, and the device that lets you see the file system, doesn't.
Oh, that maybe so. I was using iPod on usb connection for the same mp3 files. You can also compare the USB thumb drive vs bluetooth. In my case, the same mp3 file played by those 3 methods, the Bluetooth is always inferior quality.
Yes, on a PP, to play your digital files with the highest fidelity, I think (from best to worst) these are your options (These are just my personal opinions): 1. Put your mp3/WMA/AAC files on a thumb drive, insert in PP USB port. You can use your car controls to browse your files and play. Downside: Some will find this inconvenient, especially if you have a large number of files. It does work well for long audio books, though. 2. Use your 3.5mm audio cable from your phone to your 3.5mm PP port. You then use your phone to select, play, stop, etc. audio files. Downside: You cannot use your more-conveniently positioned control buttons of your car, and the audio does not automatically stop when you stop the car (or start when you start your car). 3. Buy a Bluetooth audio receiver that supports your phone's best Bluetooth audio codec. Connect its audio output to your 3.5 mm port. If you power this device from your car, it *may* start and stop playback when your car starts or turns off. Downside: Extra cost (unless you already have). For some, one more thing to manage or misbehave. 4. Get an iPhone and use Apple CarPlay (I believe available in 2020 models of PP. Please do your own research.). 5. Buy a 2021 PP, which should support Android Auto. (Please do your own research.) 6. Use the built in Bluetooth, which will likely use the SBC codec. This is usually just fine for spoken word audio. Sadly, SBC could have been great. As it was literally defined in the A2DP standard, the original authors used very conservative (i.e. low) bit rates in order to reduce the chance of transmission issues. Later, it was observed that, in general, higher bit rate BT audio would also work. This is what LDAC and Samsung's Scalable codec do. Had people increased the bit rate of SBC, it would likely produce very usable audio. I know. I have heard it for myself. You can too: Bluetooth A2DP SBC/aptX Online Encoder If you want to learn the technical details, take a look at my article:
This gives me an idea for a hack. It should theoretically be possible to replace the 3.5 mm aux in connector (presumably TRS) with a TRRS connector that would allow for playback control. Then interface that with the steering wheel buttons somehow. Sort of like this, but using the steering wheel buttons. Build a Cable to Control Your Android Phone While You Drive
Sounds like a fun project. But if you just want something that works, search for "phone audio remote control" at your favorite online store. Look for a device that just does the control, but doesn't require you to use bluetooth audio. So, the idea is wired audio, but wireless control.
Higher sampling rates and but depth were grayed out, so I can't find any way to set it to higher quality. To be clear 44.1kHz 16 bit is good enough for car audio, but I thought maybe forcing it to be higher would also force higher bandwidth or a higher cutoff frequency.
Actually, despite your intuition, that won't help. The big issue with SBC codec (and most BT A2DP audio codecs) is that the codec is initialized at too low of a bitrate. I am of the philosophy that 44.1 kHz 16 bit stereo is plenty good not just for car audio, but any 2-channel audio. I have yet to encounter anyone that can pass an ABX test showing otherwise. From my memory, my 2020 PP only supports the SBC codec. While it advertises the ability to have higher bitrate SBC audio, it does not make any sound when you try to push higher bitrate SBC to it. This is common, as most developers do not test or confirm compatibility with the spec. SBC is a sad story of "good enough for most" being the upper-bound of what the rest of us can get.
