Up the ante with high-resolution audio
If CD quality isn't good enough for your ears, you can raise the resolution even higher with lossless formats.
With digital audio, analog sound waves need to be translated to digital information. The amount of raw information included in a file depends on both the bit depth and the sample rate. The bit depth describes how much data is used for each sample of audio: 16-bit audio offers 65,536 bits, while 24-bit audio captures 16.7 million bits. The more bits, the more accurately the digital signal approximates the analog signal it represents. A CD has 16 bits per sample, for example, while a Blu-ray DVD uses 24 bits per sample. Likewise, the sample rate indicates how often the analog sound wave, which is continuous, is sampled in a given time period. CDs use a 44.1-kHz sample rate; Blu-ray ups it to 48 kHz. But some files include sample rates of 96kHz or 192kHz—and some people believe the extra information makes a difference in how good the resulting audio sounds. Whether or not you can tell the difference depends on the equipment you're using, how good yours ears really are, and how good the source material is to begin with.
To obtain a true high-resolution file, you have to start with a source that offers higher resolution than a CD—ripping a file from a CD into, say, a 24-bit, 96kHz FLAC file won't add anything. You can also buy high-resolution digital files from sources such as HDTracks. Of course, the more information you add, the bigger the file becomes. A 24-bit, 96kHz FLAC version of Sonny Rollins's song "St. Thomas" fills up about 143MB of space. (Whereas lossless audio has become a bit more mainstream, high-resolution audio is being pushed by the audio industry but remains a hard sell.)
Apps such as VLC for iOS and Onkyo HF Player can play high-resolution files, but there's a catch: What you can hear on your iOS device is limited by its headphone jack, which is capable of reproducing only CD quality (16-bit, 44.1kHz). Even AirPlay is limited to CD-quality audio (although it can handle 24-bit and 48kHz for video).
To unleash the fidelity of high-resolution audio files through your iOS device, you need a specially designed external digital-to-analog converter. Unfortunately, few DACs are designed to work with iOS devices. V-moda's $598 Vamp Verza is one option; Astell & Kern will soon release the $300 AK10 portable DAC, which connects directly to your device's Lightning port and enables 24-bit, 96kHz playback. Other USB DACs, such as Audio Engine's $189 D3 24-bit DAC, aren't made to connect directly, but you can use Apple's $29 Lightning to USB Camera Adapter in between.
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