(Image: Shutterstock / SergeyBitos)
Lossless audio is great, if you can listen to it. High-res tracks might start with high bitrates and sampling rates at the source, but there are many links in the chain between your music streaming service and your headphones or speakers where those numbers can abruptly drop. Listening to lossless music isn't quite as simple as just paying a few extra dollars a month, and if you don't take care, you might be wasting your money on that premium subscription. Here's what you need to know about high-res audio streaming.
Analog to Digital to Analog
Sound is analog. That's a fact that applies even when artists record their work on a computer. Turning that analog sound into digital data is how music can be saved on hard drives and streamed to phones in the first place. After that, the digital information has to be converted back to analog so you can actually listen to it.
The most common process of converting a continuous analog signal to a digital one is called pulse code modulation (PCM), and it's how most audio track quality is described. PCM involves capturing the sound wave in samples, which are like snapshots of the audio signal at a precise moment in time. Thousands of samples are needed to reproduce just a second of audio, and the more you can capture and store, the better it sounds because the more accurately the sound wave can be reproduced. This is measured as a track's sampling rate, in kHz (kilohertz, or thousands of cycles per second). The most common sampling rates include 8kHz for phone calls, 44.1kHz for CD audio, and 192kHz for high-end DVD audio. These rates can theoretically get much higher, but the increase in quality becomes less and less perceptible to the human ear once you reach certain thresholds.
The sampling rate determines how many samples are taken each second, but it's only one of three important numbers in determining an audio signal's quality. Bit depth is the range of values that can be captured in each individual sample. Imagine an orchestra slowly building a crescendo from near-silence to a thunderous racket. To capture the subtlety of the gradual increase in the orchestra's volume, you need to precisely pinpoint each step of loudness for each frequency, from the tiniest scrape of a bow to the boom of a timpani.
Bit depth describes how much space in bits (the ones and zeroes that digital computers run on) each sample gets. More bits translate into higher numbers, expanding geometrically since each additional bit doubles the number of amplitude steps to choose from. A 4-bit sample only has 16 possible amplitude values, while a 16-bit sample has over 65,000. Move up to 24 bits and you get over 16,000,000.
Bitrate is the sample rate multiplied by the bit rate, then multiplied by the number of channels (two for stereo tracks, which most music is available in) and measured in Kbps (thousands of bits per second). A CD’s bitrate is 1,411Kbps (44,100 Hz multiplied by 16 bits multiplied by 2 channels), while a decent-to-high-quality MP3 might have a bitrate of 320Kbps. Below this line, audio quality tends to suffer. Generally, audio files with specs greater than CD quality are considered high-res.
Pulse depth modulation (PDM) is another conversion process that takes a completely different approach, and some audiophiles swear by it as the most faithful method for digitally reproducing analog audio. The resulting audio from this process, Direct Stream Digital (DSD), is the standard for Super Audio Compact Discs (SACDs). Technically speaking, the sample rate of an SACD is 2,822kHz, but that doesn't mean it's 64 times better than a 44.1kHz CD; the process is different (samples are considered 1-bit, for example), so the measurements involved are also different. This gets a bit into the weeds, though, and mostly just applies to SACDs; for lossless music services, you can assume that PCM-derived numbers are being used.
The Lossy and the Lossless
High-quality audio files take up a lot of bandwidth and storage space, especially when they're lossless. Lossy audio, like MP3s and most streaming services, compress the source material so it can be more easily streamed and stored. WAV files, the standard for CDs, are lossless. WAV files are much, much bigger than MP3s: A CD audio WAV file takes up about 10MB per minute, while a high-quality 320Kbps MP3 takes up only 2.4MB per minute, and a common 128Kbps MP3 only 1MB per minute.
MP3s and other non-WAV digital audio formats accomplish these feats of storage through compression, which selectively removes data from the uncompressed file to make it smaller but still functional. Each compression scheme is defined by its own audio codec, and how much they affect both file size and sound quality vary depending on the codec being used.
FLAC decreases a WAV file’s size by only about half, but it also leaves the audio quality more or less untouched and is considered lossless. However, most codecs, like MP3 and AAC, are considered lossy because they compress the data so much that the sound quality starts to drop off. Even lossy codecs can accommodate a wide range of sample rates and bit depths, though, so you can still end up with high-quality compressed music as easily as terribly crunched tracks.
As a general rule, a lossless file is an uncompressed file (or one that you encode using a lossless compression process), and a high-res file has specs higher than 16-bit/44.1kHz, even with compression. And as another general rule, neither of them will sound as good as they can if you're listening to them on Bluetooth headphones.
The Wireless Problem
We have a separate article that explains how common Bluetooth codecs work, so we won’t repeat that information here. The most important takeaway is: There is no such thing as a truly lossless Bluetooth codec as of 2022, only lossy and less lossy. The best codecs for audio quality are AptX Lossless, LDAC, and LHDC, but even they aren’t truly lossless. That's a problem when it comes to streaming lossless audio to a pair of true wireless earbuds via Bluetooth.
Apple Music lets you select the quality of your audio streams in the Music section of the Settings menu on iOS devices or in the Preferences section of the Music app on your computer: AAC (16-bit, 44.1kHz, and 256 kbps), ALAC (up to 24-bit, 48kHz), or ALAC High Resolution (up to 192kHz). ALAC is Apple Lossless Audio Codec, Apple's proprietary media format and what you want to select to listen to lossless audio on the service. But even with ALAC High Resolution selected, the ALAC files are only getting sent over your internet connection to your phone or computer; they aren't what gets streamed over Bluetooth to your headphones. When your playback device transmits those lossless tracks over Bluetooth to headphones that only support AAC or SBC (like all AirPods currently), the quality ratchets down because it has to use either of those lossy codecs.
This means no AirPods (not even the $549 AirPods Max) are capable of playing ALAC files back at ALAC specs, because they use Bluetooth and only support up to AAC specs. Your phone might display the Apple Lossless logo as it streams ALAC files (which is technically true if you select one of the higher-end streaming options), but those files will get encoded to AAC for the wireless ride to your headphones.
Even with wired headphones, you might not be getting the highest-quality audio. Apple doesn't display music specs while you're streaming music, so you can't check the bit depth or sample rate for the current file in the app, but it will warn you about the need for an external digital-to-analog converter (DAC) to stream audio at the top level. If you don't have a DAC that can reproduce the higher sample rates and bit-depth of the ALAC High Resolution files, you might only get a 16kHz, 44.1k stream, which is technically lossless but not "high-res." A good DAC is needed if you want to listen to 24-bit, 48kHz-and-up streams.
If you’re listening to lossless Apple Music tracks on your computer or phone with an external DAC capable of high-resolution audio and pair that with a high-quality set of wired speakers or headphones, then you're getting the highest audio quality. But once you involve Bluetooth, the situation changes. Apple products work only with the SBC and AAC codecs, neither of which are capable of handling ALAC files at their full quality. So, to put it simply, you are no longer getting that high-res, lossless stream.
Alternatively, you can opt for Wi-Fi speakers, like Apple's own HomePod, that don't rely on problematic Bluetooth codecs. But there’s no guarantee that they won’t implement DSP (digital signal processing) that squashes the very dynamics you seek to preserve with high-res audio files. So, wired audio is still currently the best way to preserve sonic integrity.
Now, this isn't just an Apple or Apple Music issue—all Bluetooth playback of high-res media streaming platforms is lossy as of this writing. High-end Bluetooth codecs, such as AptX Lossless and LDAC, all suffer the same issues to varying degrees.
The Best Wired Headphones for Lossless Audio
Lose Bluetooth, Get a DAC, and Check Your Settings
Short of any miraculous new codecs appearing and becoming widely implemented on headphones, there's no way to play lossless audio over Bluetooth no matter what music streaming service you choose. In fact, you should err on the side of caution and go wired if you really want lossless music. A portable DAC for mobile devices, or a full-on amp/DAC combo for desktops, can certainly enable you to experience the full effect of lossless audio streaming services. Just make sure to check your settings to confirm the streams are the highest possible quality.
With that in mind, check out our favorite headphones for audiophiles, including a mix of both wired and Bluetooth options. If you've been scared away from Bluetooth by everything you read here, see our list above or head over to our story on the best wired headphones we've tested to ensure your lossless music is indeed lossless.
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