Mp3 playback quality via SD

[nectarguru]

This is for any audio geeks that might be here. The Fender audio system sounds amazing, even enough so to impress an audiophile friend of mine. I love it to death. That, along with the SD card reader to play media is a dream of mine in a car, and after owning a Mk4 with an aftermarket stereo and completely shot speakers, I'm ecstatic about owning my SE. Early on after purchasing, I would stream music from Spotify via bluetooth, but since then I've bought a large capacity SD card and have been ripping my CD collection. I've been sticking to 320 kbps as it's still a great bitrate (as far as Mp3 is concerned), and flac would just be impractical for space.

I've noticed, though, that the playback quality drops considerably when playing from an SD card. The other day I did a back to back test with an electronic album. Lots of bass, wide range mids and highs. My CD rip sounds almost like a big flat sound filter has been dropped over the music. The bass is there, but has no life. I cranked the subwoofer to 9 and it barely made a pop. I then flipped over to the Spotify stream of the album, and it opened up. The range was there, and the subwoofer shook the car.

I'm not trying to compare mp3s to Spotify with this thread, but I'm wondering is there a known issue of the SD card playback "dumbing down" the audio? Spotify streams at 320 kbps, and even if it doesn't, it's a night and day difference to my CD rips. It doesn't make much sense to me, because the SD card is just a tool to house the files and it shouldn't affect playback, but...?

 

[waspie]

I know ripping audio to mp3 is pretty braindead simple, but have you tried listening to the files from the sd card in anything else to see if perhaps something happened in the conversion? I ask because it sounds like thats about the only other place to look...

 

[andyrooski17]

One potential test, if the car can handle MP3 CDs (not burned audio CDs):

Load the same mp3 on the SD card and the MP3 CD and try playing both, see if there is a difference. I also second waspie's suggestion of listening to the files from the SD card on some other sound system.

I personally don't listen to music this way in the car, but, in principle it should work. It is very possible that the mp3 decoder software in the car isn't great.

Another possible test is to rip a few tracks at 128 kbps and try them. In my experience, the difference between 128 and higher bit rates is pretty subtle (especially when driving in a moving car!). It would be weird, but not inconceivable, that the decoder in the car is somehow optimized for 128 kbps, or is somehow memory-limited, such that it does weird things to 320.

 

[andyrooski17]

Follow-up, this is fun:

http://www.npr.org/sections/therecord/2015/06/02/411473508/how-well-can-you-hear-audio-quality

 

[nectarguru]

All of the music I've ripped is at 320 kbps at 44100k sample rate. One thing I forgot to mention is that a handful of the music I've loaded up were redeemable downloads from purchasing the vinyl copy. All of those albums are also at 320/44100, but one was flac which I've converted to 320 (although I've heard that the car will run flac, which I'm going to try). I also loaded up a good chunk of 320 mp3s which I've collected over the years.

All of them sound relatively the same (flat), but one of the vinyl downloads does sound pretty good. One of my reference points here is the bass, because if I crank it to 9 I barely hear a change, but for this particular album the subwoofer is very responsive.

Right now I'm leading towards andyrooski17's theory about the car being optimized for 128 kbps. I'm going to be running some tests on this when I get some free time later in the week. I'll take 3 tracks and load them onto my phone, iPod, and SD card, then do an ear test comparing them to Spotify. I'll report back.

 

[nectarguru]

Oh, and waspie, I haven't tested the tracks on another sound system yet, but given that some of these tracks are from other sources than the cd, I don't think there'd be much change. But that's just my opinion.