AAC (Advanced Audio Codec - MPEG-4 Layer 3) is a standard audio codec licensed by Fraunhofer. Licenses are for manufacturers only. No licenses are required to stream or distribute content in AAC format. AAC today is widely adopted across the industry, including by Sony, Google, and Microsoft, and supported by all major operating systems (Windows, macOS, iOS, Android, WebOS, etc.).

ALAC or Apple Lossless Audio Codec, was introduced in 2004 and is a very similar lossless compression scheme to FLAC. And although ALAC was developed by Apple for Quicktime, it is open source since 2011 and available royalty free. It was introduced on iTunes and the iPod, and is supported today on the iPhone, and for wireless audio streaming over AirPlay (over Wi-Fi) on all Apple devices. The compression scheme (approximately 2:1) and the decoding is very power-efficient, ideal for portable players and smartphones. Being open source, any manufacturer (hardware or software) can easily add support for ALAC.

But it is important to note that, when discussing lossless, there are no “lossless” codecs available over Bluetooth. Even if there are codecs supporting hi-res audio (24-bit or higher than CD-quality) such as Sony LDAC and Qualcomm aptX HD, they are not lossless and all are constrained in the same way by the bandwidth available on the Bluetooth radio (990kbps for LDAC, 570kbps for Qualcomm aptX HD). That is not very likely to change, even though the Bluetooth SIG is working on new upcoming specifications that might determine support for new optional codecs. But any new codecs, as Qualcomm and Sony learned, need to be supported on the source and sink sides. For Apple that could be easier to do, but not as a “lossless” format over Bluetooth. It is always more effective to use AAC or even the new LC3 codec adopted in Bluetooth LE Audio, which might improve transmission efficiency but will not affect the subjective quality impression of the original stream (even with a few removed bits...).

The big advantage with AAC is in the fact that all services streaming AAC files (and it's not only Apple, but many others also using AAC) are transmitted via Bluetooth as AAC with no further compression/encoding needed. Sending a hi-res FLAC file via aptX HD or LDAC over Bluetooth always requires further compression and is not as power-efficient. Same with ALAC files, which are transmitted as AAC over Bluetooth (or SBC if it’s not an AAC-capable device). Note also that, even if a system supports multiple codecs, it’s not always easy for consumers to “choose” which ones they will use.

Audio originated in high resolution can be transmitted or streamed using an uncompressed format, lossless codec, or lossy codec (such as the ones supported in Bluetooth). So, ALAC streaming (like FLAC) and any uncompressed material are currently the “convenient” and practical solution for a streaming service played over a wired sound-chain to compatible equipment. Will it be possible to stream uncompressed audio - over 5G networks, as an example? Yes, but not practical for mobile devices, and that is were the industry focus is - mainstream services.

And that is always the most important perspective when discussing high-resolution audio or even codecs. Hi-res Audio for what? Recording? Storage? Transmission? File Downloads? Streaming? How? Over USB, Ethernet, Wireless Wi-Fi, Bluetooth? All are different discussions with different requirements and constraints. Also, it is important to always situate this debate within “digital.” (I do cringe every time I see a comment - sometimes from people I deeply respect - about how “analog media” stores higher fidelity, etc. That is not helpful for clarification of the topic in question. We are discussing audio that is already in the digital domain).

And to further complicate things, these days, every time there is wireless transmission of high-resolution audio formats involved, even over Wi-Fi or proprietary schemes such as DTS Play-Fi, users should check if the original source format is supported and if any decoding/re-encoding is required. Transmission of uncompressed audio is the ideal, but when the source media is already compressed, even if using a lossless codec, this needs to be considered.

I was also asked why some files stored on streaming services are better than others. There are so many variables to that question that it is hard to answer. But I would just start by differentiating from a file that was submitted by an artist or record company (normally a 24-bit/96kHz PCM/WAV file as defined in the Apple Digital Masters guidelines, for example,) and the file that is being made available for download or streamed. Two different things, which should never be confused, with many variables in between.

Also, different streaming services have harvested those music libraries from multiple sources, so the requirements have been varied and many early services did not care to request the “best possible quality master.” Many have accepted mainly only standard Redbook CD-quality (16-bit 44.1kHz). It’s even possible that a lot of music was delivered with some form of compression - and that is all there is in the library. The variables are just too many to detail.

What I would like to highlight is this. The original file that is stored by a music service and the file that we get on streaming services are different things. But if offered with lossless streaming, we know that what is offered at the source, is what I receive in my end. That is why it is “lossless.” If it’s hi-res, it’s hi-res, if it’s not hi-res, it’s not hi-res. Debates about “my FLAC is better than your FLAC” are pointless. If there is something about that to consider, I want to see the research.

As I said in the Apple Music announcement published online, for many years, Apple was the only company storing only uncompressed 24-bit/96kHz digital masters of all the music that was uploaded to its servers. There is no question that the Mastered for iTunes guidelines and subsequently the Apple Digital Masters program - which included free mastering software tools - were decisive to encourage musicians and record labels to stop considering the CD-quality (16/44.1) deliverables as the "master."

Before iTunes (iTunes was launched in 2001, but its major impact wasn't felt until approximately 2007 with the DRM changes), many studios that recorded 24-bit, at whatever sampling rate, would mix and master for the Redbook CD standard and that was it. In the same way that previously, millions of records recorded in very high quality multitrack analog tape were mixed to 1/4" stereo tape masters, which is what was kept (multitrack 1" tape was expensive and studios recorded over and over again using the same tape, unless the client paid to keep the multitracks).

Only after Mastered for iTunes (2012) the mindset changed. Even independent labels switched to consider 24-bit/96kHz (or more but that was not for everyone) as "the master" and uploaded those files. The practice became mainstream at that time. Before that, of course, there was a lot of music recorded in 24-bit/192kHz and there was the DSD crowd, but together that doesn't make more than a small percentage of the music released. The catalog for hi-res only expanded dramatically from there. But thanks to Mastered for iTunes, Apple got the head start.

This also means that in fact, many of the best recordings we have now, are the few high-quality analog masters that were digitized directly into hi-res. Between the late 1980s and 2012, when CD masters were predominant (and the first 10 years of CD masters suffered from the really poor AD/DA converters available then) there is very little hope to improve the quality, unless some miraculous tape was kept. Why anyone would still be submitting CD-quality “masters” today is just stupid, since there will be no CD release. I’m not debating if it’s “good enough” or whatever. The point is - if I recorded and mixed in 24-bit/96kHz or more - I should always consider my master in that format, never bring the quality down. But not keeping the original hi-res recording sessions would be beyond comprehension.

In reality, for everyone working with DSD, Super-Audio CD in the 1990s, and henceforth devoted to exploring the possibilities of digital recording and distribution in the highest quality, this announcement by Apple seems to be many years overdue. And comparatively to what we had with SACD, having lossless streaming doesn’t seem like a big deal, but that was the price to pay for the transition from physical media to file downloads and streaming. Now, we need to take it from here and never look back.

Of course, the topic of high-resolution audio over Bluetooth needs to be saved for a future article. Yes, there is no high-quality “lossless” option for transmission over Bluetooth. But it’s important to highlight that AAC supports high-resolution audio since its inception. Useful reading on that topic is available in this paper.

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