Music has been helping drivers slog through commutes and rock out on road trips ever since cars became civilized and quiet enough to hear it. But have you ever wondered if the sound quality of music stored on your phone is as good as your CDs? Testing shows that the answer is a qualified yes.
Automotive audio systems have come a long way since Consumer Reports gave in-car record players a spin back in the 1950s. Formats have also evolved, and with music stored on smart phones threatening to send automotive CD players off to rock-and-roll heaven to join the mobile phonograph and cassette player, we thought a comparison test was in order.
To evaluate various listening options, we gave two dedicated Consumer Reports audio engineers the keys to our Mercedes-Benz S550 test car. They brought along two 5th-generation iPod Touch digital music players loaded with specially selected test music and a reference CD for comparison. We chose the S550 because its quiet interior and high-quality Burmester audio system were likely to bring out fine differences in sound quality. If the trained ears of our audio specialists couldn’t detect a difference in the Benz, we reasoned that chances are most listeners wouldn’t notice a difference in their cars.
Each of the iPods contained the same six tracks, copied as digital audio files in AAC (Advanced Audio Coding) format at bit rates of 320, 256, 128, and 64 Kbps (kilobits per second).
In laypersons terms, the higher the bit rate, the better the sound quality, because more of the original music is captured. The downside is that larger files take up more storage space in your music player, thereby limiting the number of songs you can store. To put the numbers into perspective, 320 Kbps is the highest AAC bit rate setting in iTunes, 256 Kbps is typically used for paid music downloaded from online music stores, such as iTunes and Amazon.com, 128 Kbps is the default setting for copying audio into iTunes, and 64 Kbps is the lowest AAC bit rate setting in iTunes. (Streaming music bit rates vary widely, depending on source, connection, and device.)
We also recorded our sample tracks in WAV (Waveform Audio File Format). These are uncompressed files that contain the same audio information as the original track and are theoretically identical to the original CD. The downside for that quality is that the large file size uses a lot of digital music player memory, and as our testing revealed, the benefit may be purely theoretical.
One player was connected to the car’s audio system using a USB data cable; the other was wirelessly connected to the car’s audio system using Bluetooth. The engineers than tried different listening options with the car parked, at 25 mph, and at highway speeds.
What we found
In our test car, there is no significant difference in sound quality between the CD and WAV, 320 Kbps AAC, and 256 Kbps AAC audio files. We would expect similar results for MP3 files recorded at the same bit rates.
Where the sound quality difference became noticeable was at 128kps. But even then, the reduced clarity was not really noticeable without focusing on it. At 64 Kbps AAC, the differences were more noticeable, with compromised sound quality.
We found no significant difference in sound quality using either the USB cable or Bluetooth to connect to the test car’s sound system. This may not be the case for other cars, but if you have these two connection options in your vehicle, it’s easy enough to compare them yourself.
Bottom line
If the music stored on your phone or other digital media player is saved with a bit rate of 256 Kbps or higher, you won’t be giving up any sound quality by leaving your CD collection at home. Some listeners will probably be perfectly happy with 128 Kbps. The best bet is to do your own experimentation. Make your own compromises between space and sound quality based on the music you listen to, the car, and the audio system. When it comes to rockin’ the road trip, we think 256 Kbps is the sweet spot.
—Jim Travers
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