After we got the Bose Quiet Comfort 20i noise-canceling earbuds for Jeannette, I decided to sit down and compare them with my Bose Quiet Comfort 15 noise-canceling headphones, my Shure E3 in-ear monitors, and my Yamaha YHD-1 orthodymanic headphones. I was actually somewhat surprised by the differences between them, and I thought that they all sounded fairly good by themselves. I think that the Bose earbuds and headphones were very similar. I thought they my Shure E3 had better clarity, though the Yamaha sound was more open and natural, but lacked a little low-end.
While researching the earbuds, I ran across numerous articles on high-resolution audio as well, which is loosely anything that is more than the 44.1KHz sample rate with 16-bit depth (16/44) used by CD recordings. While many of the articles proclaimed how 24/96 or 24/192 sounded so much better than the overly compressed 16/44 recordings. I also found a number of articles like this one proclaiming that HD audio is like the modern-day equivalent "snake oil" marketing hype like tubes vs. transistors or oxygen-free speaker cables... Kirk McElhearn points out that at 16-bit, you can record up to 65K volume levels, and that 44KHz is the minimum sample rate to capture frequencies up to 20KHz, the standard for high-fidelity audio.
If you think back to the time when we went from 256 colors, to 65K colors to 16.7M colors, the difference was dramatic, with 16.7M colors more life-like and photo-realistic. While we were mostly content with 65K colors, and probably can't detect all 16.7M colors, the optimal color bit-depth probably lies somewhere in between 65K and 16.7M.
I think that the move to high-definition television is similar in many respects. In addition to being a higher pixel resolution, the image is also more realistic due to the improved color depth, with better shadowing and high-lights that also gives the image more depth. This change isn't just the resolution alone, but a combination of factors that makes the image discernibly improved, even when comparing 1080p to 720i resolutions.
Kirk McElhearn also had an article describing how to properly change the settings on the Mac to listen to high-resolution audio files, by changing the maximum bit-depth and sampling rate. He also points out that your sound quality is only as good as the weakest link, so if you're using cheap earbuds or speakers, you won't be able to detect any difference, much like trying to watch a Blu-Ray movie on an older analog TV wouldn't look any better than a DVD or a VHS tape.
Kirk also talked about the differences in the audio file format and compression used in MP3, AAC, Apple Lossless or FLAC, and uncompressed AIFF files. I was curious if I could detect the difference, so I took a CD and imported the same track as an MP3 and a 256Kbps AAC file. I found a free application in the Mac App Store called ABXTester which lets you do a blind comparison of two files in different formats, as long as they are natively supported (so no FLAC, for instance). With my Shure E3 in-ear monitors I was able to discern the difference between the higher and lower resolution files 4/5 times in repeated tests, which was enough to convince me that I was able to hear the difference. I re-imported the same CD using Apple Lossless, and was again able to pick which samples were which resolution more than 80% of the time.
Looking at my iTunes library, and displaying the columns for kind and bit-rate, I realized that most of my music was in the lower quality AAC (128kbps bit-rate), likely the default that I picked when my primary iPod was only 15Gb storage capacity. Even though higher rate formats were available, I hadn't changed the default, since that gave reasonable quality with a manageable file size, so that I could fit the majority of my music library on the iPod, without having to pick and choose what to include or exclude.
Over the next few weeks, I re-imported all of my CD collection into iTunes using Apple Lossless format, which preserves the quality of the audio, while allowing some compression to reduce the file sizes. I also changed the settings for synching my little iPod touch to convert down to 128K AAC, but 256K AAC on my iPad which has much more space available. This lets me have the highest quality on my MacBook Pro at home, with a more manageable size on my portable devices.
During this time, I also researched options for better quality headphones, using some of the same websites where I researched the noise-canceling earbuds. I prefer an over-the-ear style for more comfort when using the headphones for a longer period of time, and wanted an open-back design to use at home, since I already have the Bose QuietComfort 15 to use in noisy situations. I spent a lot of time reading through the reviews of full-size open-back audiophile headphones at InnerFidelity.
I was impressed to see that a decade old design costing under $300 on sale, the Sennheiser HD600, still made their "wall of fame" list, along with newer high-end headphones costing over $5,000! I've liked the professional audio gear from Sennheiser that I've used before, particularly their wireless microphones, and they are certainly widely regarded for their headphones. I also liked that many of the parts like the headband, ear pads and cables are replaceable, and sometimes interchangeable between similar models like the HD650.
The one drawback to the HD600 that I recognized is that the nominal impedance is over 300 ohms, which means that many low-power portable devices would have a difficult time driving them effectively, as they don't produce enough output power to drive that high of a load. That lead me to look for a headphone amplifier. While my intention is to primarily use the headphones at home, I wanted the option of a portable unit that I could take with me if I moved around the house. I found several portable headphone amplifiers that would work, but also discovered that for not much more than the price of an amplifier, I could get a unit that contained a higher performance Digital/Analog Converter as well, which would allow me to playback high-resolution audio files if I chose.
After some more research, I settled on the TEAC HA-P50 portable headphone amplifier/DAC. It's about the same size as the original iPod, with a large enough battery to last as long as my iPod Touch or iPad Air, and with a variety of inputs, including analog, TOSLINK, and USB. It comes with a high-resolution audio player on the Macintosh and for iOS, and allows USB connection to Windows, Mac, iOS and Android devices, so there is plenty of flexibility. It also incorporates its own Digital/Analog Convertor chip, a TI PCM5102 "Burr-Brown" unit that supports high sample rates and bit-depths.
I've been very pleased with the combination of the Sennheiser HD600 with the TEAC HA-P50. I think that i would have been very disappointed with the sound of the Sennheisers without the headphone amp. I do believe that the Burr-Brown DAC sounds better than the built-in DAC in the MacBook Pro or iPad, which also don't have enough power to drive the high-impedance load of the Sennheisers. I have done some comparison of high-resolution file formats, and with the HD600's, I can hear a difference in the sound quality. It is often subtle to be sure, but the HD audio has a more open, natural sound, with a more ambient, airy feel, where each voice or instrument can be discerned separately, instead of blended together in the lower-resolution recordings. You can hear the timbre of the horns, the resonance of the string bass, etc.
I can tell a significant difference with many of the CD recordings that I've had for years, re-imported using Apple Lossless format, played through the TEAC HA-P50 driving the Sennheiser HD600 headphones. Even live recordings like Kenny Loggins "Live from Under the Redwoods" has much better clarity, such that you can hear each voice in the chorus, instead of a single, blended voice.
I have downloaded some comparison samples from SoundLiaison and HDTracks.com which allow you to compare the same tracks in different formats. I've also purchased a few albums from HDTracks at higher resolution to compare with some of the CDs that I already owned. Anita Baker's "Rapture" has more clarity in HD audio than on the CD. I've just purchased a 24/96 high-resolution copy of "Chicago II" that is remarkably better than the same tracks from the "Greatest hits Volume I" CD that I've had for years. While it is likely a combination of factors, including not only the resolution and bit-depth of the recording, but also the engineering with little or no compression, etc. that makes the HD Audio recordings sound better than the CD recordings, I can tell a dramatic difference.
While I am still using iTunes to manage my music library, as it allows me to organize and synch my music with my iPod and iPad Air, I've switched to using the free music player VOX to listen at home, as it supports additional file formats, including FLAC and DSD or DFF, and support the high-resolution formats, and will synch the resolution of the TEAC's DAC to match the recording.
I think that the higher resolution and bit-depth capture more nuances in the sound than you get in the CD quality recording at 16/44. It's not just about frequency response, but the level of detail, provided that you have a high-quality sound system that is accurate enough to hear the differences. A good pair of headphones and an amplifier/DAC combination can be had for less than $500, allowing an audiophile listening experience without a lot of investment, which is still portable.