the Hearts of Space studio
We don’t get that many inquiries about high resolution audio, but recently one of our subscribers asked us about the audio quality of current HoS streams and why we don't offer a "high-res" service. I'd been meaning to write it up anyway for HoS News, so here goes. It's unavoidably technical, but if you care about digital sound quality, most of the terms and concepts should be familiar.
The national HoS program dates from 1983, which was the waning days of the analog audio era. So roughly the first 100 programs from 1983 to 1986 were produced on quarter inch analog tape. Master tapes in those days ran at 15 or 30 ips (inches per second), but we were forced to work at 7.5 ips because we were making 59:00 programs, not three or four minute songs, and a show had to fit on a standard 10.5" reel. The lower speed limited the ultra high frequency quality of our program masters slightly, but was perfectly acceptable for radio programs. Ironically, the low-end bass performance at 7.5ips was actually better than 30ips masters.
Most of our source material came from LPs, occasionally from master tape copies direct from the artists. In those cases, if you could ignore surface noise from the LPs (I couldn't) the quality of the original sources was pretty good. When cassettes became popular, things got worse for a few years. Many of our new age titles had to be dubbed from high speed duplicated cassettes with limited bandwidth and dynamic range and significantly more noise. Nevertheless, with careful engineering, everything sounded "listenable."
We got into digital as soon as it was practical, first using the Sony PCM-F1 digital recorder, and later the Sound Designer 2 computer program and its successor Pro Tools, which allowed us to do precision digital editing. Even these early digital recording systems offered substantially better audio quality — orders of magnitude less noise, distortion, and speed instability, and absolutely "flat" frequency response — and replaced our original analog tape production system. The commercial CD was introduced in 1982 and took almost ten years to completely replace LPs. So during the 1980s our production system was increasingly rationalized around the CD format. That means stereo, 16 bit (word length), 44.1 kHz (sampling rate), linear PCM (Pulse Code Modulation) format — i.e. the so-called “Red Book” CD standard.
Then and now we transfer music from CDs or digital files into Pro Tools at 16 bit/44.1 kHz, edit or remaster as necessary at 24 bit internal resolution, mix in the voiceovers and then output our program masters at the same resolution: 16 bit/44.1 kHz in BWAV (Broadcast WAV) format. So our production system is 100% “lossless” as far as the music is concerned. Even in the few cases where an artist or record label supplies us with a higher resolution PCM original like 24 bit/96 kHz, we have to down-convert it to CD format to work with it in our production system.
If you are an audiophile and you are looking for true high-res digital audio, HoS is not currently able to provide it, for several reasons:
• Artists may produce their recordings using higher res formats,
but the vast majority still release in 16 bit/44.1 kHz.
• True high-res formats are bulky: they can be up to 10x larger
than CD standard digital audio and require special hardware
and software to play.
• High-res originals are still difficult to stream due to bandwidth
limitations on typical broadband networks.
• If uncompressed CDs are streamed, the bit rate is 1411.2 kbps
or approximately 10 megabytes/minute. High-res digital would
typically be 2-4 times greater, i.e. similar to HD video bit rates.
• Bit rates like this are possible for desktop machines with direct
broadband connections, but these days people also want to listen
on WiFi on their phones and tablets, "smart speakers," and in their
cars over the cellular network, where these heavy bit rates cannot
always be supported reliably.
• Aside from the occasional audiophile, there has been no demand
from the rank and file HOS audience for high-res streams;
especially at higher prices; especially now!
So the original sources we use today are standard uncompressed CDs, WAV or AIFF files at CD resolution, OR "lossless" (data-compressed) FLAC or ALAC files that expand to uncompressed 16 bit/44.1 kHz WAV. Occasionally, we may have to use a compressed stream file as the source, normally AAC (Advanced Audio Codec) format at 16 bit/44.1 kHz. We do not use MP3 originals; AAC offers audibly better quality at every bit rate.
To stream them to you, our distribution chain starts with our Hearts of Space program master files in BWAV (Broadcast WAV) format — uncompressed linear PCM at 16 bit/44.1 kHz, exactly the same as CDs. For streaming, the programs are encoded in AAC format (technically a "lossy" codec) at 256kbps, 128kbps, 64kbps, and 40kbps, and then "packaged" into the HLS (HTTP Live Streaming) "adaptive bitrate" transport protocol for delivery to the public.
Which of the four available resolutions in the HLS package a typical listener will hear depends on the device they are using, the speed of their internet connection, and network conditions. In most cases, users will hear the 256kbps streams, which are very close to CD quality. The HLS protocol will seamlessly drop down to a lower resolution file "on-the-fly" if the client device is not able to keep up with the bandwidth demands of the higher res file. This is one of the reasons that HLS has become the industry standard for streaming audio.
There are a number of streaming music services that offer true high-res digital audio files in several different formats, including TIDAL, QOBUZ, DEEZER HIFI, PRIMEPHONIC, and AMAZON MUSIC UNLIMITED. The music offered varies, from millions of tracks across all genres to specialty collections.
Clearly, Hearts of Space is specialty collection focused on a specific kind of musical experience, which we describe as "ambient, space, and contemplative music from around the world and across the centuries." Because of this broad focus, it would take a great deal of time and manual work to assemble a personal collection of "HoS-type" music on one of these high-res services, and it would still not be as comprehensive or meticulously curated.
I'm confident that at some point in the next few years Hearts of Space will be able to offer high-res service for at least part of its repertoire. In the meantime, we recommend that audiophiles maintain two streaming subscriptions — one to a high-res service for absolute audio quality, one to Hearts of Space for a unique musical experience.
Safe journey :: Stephen Hill
