HIGH RESOLUTION AUDIO and Hearts of Space

 

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

Comments

[Jack Aldrich]

I've been enjoying Hearts of Space since the late 70's when the KPFA radio show version known as "Music from the Hearts of Space" became the epicenter of my musical experience.

Over the past 40+ years, Hearts of Space has provided me the highest-quality broadcasts possible despite many technological complications. Ultimately it is the quality of the curation, the depth of the source content and the ongoing celebration of this remarkable genre of music that defines HOS as a great treasure that continues to satisfy and heal.

Thank you for your efforts to share these wonderful works with us. Blessings and deep gratitude. - Jack Aldrich

[James Wilkinson]

And here we thought all you did was throw a record on a turntable and record it...!

[Zach Schudrowitz]

This was interesting to read for the technical steps. I'm sure there's even more work that goes into it. "CD quality" has always been good enough for me. I think to get the higher res quality, you also need to have better speakers/headphones. Most of the time I'm playing it on my iPhone speaker and any hi-res stream would be lost on me. Thanks for a look into the technical window of creating the program.

[David Auerbach]

Given how much our hearing degrades as we age, there's not much benefit and if the music is created with synthesizers, vs. a physical 'analog' instrument, what should it really sound like? NPR has a test you can take to see if you can distinguish bitrates (www.npr.org/sections/therecord/2015/06/02/411473508/how-well-can-you-hear-audio-quality).

[Daniel Sibo]

Pack rat that I am...I found a box with the MftHoS Program Playlist- Summer 1985 and all of the Program Play Lists (mid 1980 onward) and Catalogs that I sent my "self addressed stamped envelope" and $1 away for. The first program we heard was 101 Zithers. Good times, great music. Thanks for all the bliss.

[Chris Hansen]

I've been listening since nearly the beginning, in New York, Chicago, San Francisco, and now in London. I appreciate the fact that you have actually thought about this question, considered the best course of action, and can explain it in terms that this music lover but audio noob can understand.

I should guess that within a few years the high quality streams will become commonplace, but until then I'm happy with the quality of the music on HoS, and that includes not only the audio quality but also the quality of the selections you stream. Thanks for giving me so much pleasre over the past 40 years or so.

[Noah Green]

Thank you for the technical explanation. I have been listening to HOS since I was a boy starting in the late 1980's through KUHF in Houston, Texas.