High-resolution (hi-res) music comes in various flavors of bit depths, sampling rates, and even formats (PCM, DSD). This leads to an interesting test of capabilities when buying new hardware.
Consider a visual analogy: When high definition TV (HDTV) came out, people had to decide what "high definition" meant when it came to TV. Numbers and letters got thrown around: 480p, 576p, 720p, 1080i, 1080p, EDTV, HDTV, and even "full" HDTV. Of course, if the TV looked better when you got it home, that was the most important thing, but for a while, it was not obvious whether a HDTV was showing an HD signal -- and at least part of the issue was source-material related.
Similarly, now that we are talking about hi-res music, a common understanding has come about as to what "high-resolution" is when talking about music playback. Specifically, it tends to refer to minimums: a minimum sampling rate, and a minimum bit depth. It seems the common minimums are in place.
- Sample rates: Greater than 48kHz. Common PCM sample rates are 88.1kHz, 96kHz, 176.2kHz, and 192kHz.
- Bit depths: Greater than 16 bits. The common PCM bit depth is 24 bits per sample.
Many many words have been written as to the value of increases beyond these minimums, particularly as to their sonic benefit in relation to mastering techniques, dynamic compression, and source quality. My post really isn't about any of these things; rather, I simply want to know: If a hardware manufacturer says I'm getting hi-res music, am I really? Part of the answer to this question amounts to a test of capability, because that is what is being advertised -- higher sampling rates and more bits per sample.
Portable hardware manufacturers of digital audio players (DAPs) and digital-to-analog converters (DACs) design hardware to play back such hi-res files. Often, they tout their capabilities: 24-bit/96kHz playback or similar verbiage.
When it comes to portable DACs, however, there is an additional catch: One has to connect the DAC to the source device -- a smartphone, tablet, or computer -- using the right cables, and then use the right software or drivers to get playback to work. Hence, although one might have a hi-res DAC, it might not be the case that one is listening to hi-res audio from that DAC due to some software or hardware connection along the way.
This post describes a test of the following four portable DACs to verify their ability to play back 24-bit audio from an iPhone 5. I've left out any tests of sample rates because it is hard, perhaps impossible, to check what the sample playback rates are without test equipment.
- beyerdynamic A 200 p
- CEntrance HiFi-M8
- HRT microStreamer
- FiiO E17
I am happy to report that all four of these portable DACs can play back 24-bit audio with a resolution that is greater than 16 bits, but in some cases, it takes some finagling to make it happen. Read on to hear the full story...
Coaxing 24-bit Playback from an iPhone
The iPhone 5 under the current iOS at the time of writing (7.1.1) does not natively support high-resolution sample rate playback from files stored in its iTunes memory. For example, when you try to drag 24-bit/96kHz files to an iPhone in iTunes, you get a "this file is not supported" error, and the file does not load. This is a non-starter for most people, although it has led to an interesting technical game of trying to find the right combination of iOS app, portable DAC, and connection method to get files to be heard in their full resolution format. Then, one has to use some form of sideloading or streaming method to get at the hi-res music. This post is not focused on this problem, because there are other threads out there that discuss some of the technical issues and methods. A really good one for the iPad (and presumably with the iPhone 5 in iOS 7) is this:
For my tests, I used a Seagate Wireless Plus 1TB hard drive with the SeagateMedia app which supports both sideloading and streaming hi-res files from the Wireless Plus.
The next thing to be concerned about is how to connect the DAC to the iPhone. Some DACs are "Made for iPhone/iPad," but that does not necessarily mean they are designed for hi-res playback because of the lack of native support mentioned earlier. What others have figured out through extensive testing is that SOMETIMES one needs to use the Lightning-to-USB Camera adapter to get hi-res audio to play back. Even then, the power draw from the portable DAC can sometimes bring up the "this accessory draws too much power" message on the iPhone's display, which leads to one using some form of powered USB hub to get past the power message, or requires loading custom firmware to the portable DAC to lower its power draw. As you can see, this is all a bit of a minefield, which can be frustrating to get working.
In my tests, I ran the following five configurations for the aforementioned portable DACs:
- iPhone 5 -> beyerdynamic A 200 p (Lightning cable)
- iPhone 5 -> Centrance HiFi-M8 (Lightning cable)
- iPhone 5 -> Lightning-to-USB Camera adapter -> USB A to USB B cable -> CEntrance HiFI-M8 (USB B input)
- iPhone 5 -> Lightning-to-USB Camera adapter -> USB A to mini USB -> HRT microStreamer
- iPhone 5 -> Lightning-to-USB Camera adapter -> USB Hub -> USB A to mini USB -> FiiO E17
The first two configurations are the most elegant because they involve only a single cable that can be very short. The last three configurations are more like Rube Goldberg machines because they involve overly-complicated cabling that one has to deal with somehow in a portable setting. Here's an example of the HRT microStreamer setup:
The firmwares of all of the portable DACs are stock except that for the microStreamer, which HRT offers as a download on their website. Updating firmware can ruin your device, so I try to avoid it whenever possible unless it unlocks a capability that I need to have.
Testing 24-bit Playback
So, with the above six configurations enabled, now I needed a way to test 24-bit playback in a land of 16-bit audio. The simplest strategy seemed the best: Take a bit-perfect audio playback app, create a 96kHz audio file whose non-zero bits are never in the top 16 bits of each sample, and play the file through each portable DAC. If the DAC creates a recognizable sound from the file, then more than 16 bits are being heard, i.e. hi-res has been achieved according to the common understanding. If no sound is heard, the player is not playing back hi-res information from the file.
I created a 24-bit, 96kHz WAV file that was 5 seconds long and had a single 440-Hz tone in it. The peak value of the sine wave in integer terms was 120, which is less than 7 bits in magnitude (and thus less than 8 bits of resolution). I loaded the file into Audacity and used the Amplify function to verify its loudest value: -96.9dB relative to maximum, which is beyond the 96.3dB dynamic range of a 16-bit file. I then proceeded to play back the file using the SeagateMedia app via the Wireless Plus drive.
Now to actually hear the tone at the output of the device, I needed to add gain to the analog stage of the portable DAC in most cases. I used a FiiO E12 to do this, in a double-amping scenario. WARNING: Be careful when trying to listen to soft sounds when turning up amps -- you can damage your hearing if something goes wrong. I was quite careful in this regard and experienced no sonic accidents.
As a check, I then played back a music file that I know is 24-bit/96kHz to be sure I was getting audio out from the connection itself -- after lowering the volume, of course!
Read on to see what I found.
- iPhone 5 -> beyerdynamic A 200 p (Lightning cable) : Tone heard
- iPhone 5 -> Centrance HiFi-M8 (Lightning cable) : No sound
- iPhone 5 -> Lightning-to-USB Camera adapter -> USB A to USB B cable -> CEntrance HiFI-M8 (USB B input) : Tone heard
- iPhone 5 -> Lightning-to-USB Camera adapter -> USB A to mini USB -> HRT microStreamer : Tone heard
- iPhone 5 -> Lightning-to-USB Camera adapter -> USB Hub -> USB A to mini USB -> FiiO E17 : Tone heard
I'm happy to report that all of the tested DACs can play back 24-bit files from an iPhone 5 with information that is beyond the 16 bits of standard digital audio. And, interestingly, the beyerdynamic A 200 p can do so without the Lightning-to-USB Camera adapter. The A 200 p looks to be the most compact portable DAC available that is capable of hi-res playback straight from an iPhone. I have this DAC on loan from beyerdynamic and will have a full review of it soon.
The CEntrance HiFi-M8 is interesting in that it can do 24-bit hi-res playback, but NOT currently from its Apple-approved convenient USB A MFi input. This confirms what others, particularly ExpatInJapan, has already posted, and CEntrance is well aware of the issue and is reportedly working on it as a firmware update. Since the HiFi-M8 works with the Lightning-to-USB Camera adapter, and very short USB A to USB B adapters exist, it is not too hard to get hi-res audio from an iPhone to a HiFi-M8 currently via the USB B input. I recommend this connection if you can afford the additional bulk.
The HRT microStreamer is a niftly little portable DAC for an iPhone when paired with the Lightning-to-USB Camera adapter. As the above picture shows, it does not add much to the size of the iPhone when a short USB cable is used, and the microStreamer has the advantage of having a dedicated line out. Feeding that line out to a more-powerful amp like the E12 makes for a very nice sonic solution that is also portable.
The FiiO E17 is an interesting low-cost portable DAC but requires a USB hub to work with an iPhone currently. It is not very portable, but it can work in a pinch as a simple desktop solution if you can't use your (e.g. work) computer as an audio source device.
Getting 24-bit files to play back through a portable DAC seems to be a challenge when using an iPhone. There are rumors of changes in iOS, specifically the native support of hi-res playback. If that happens, high-resolution music playback will likely get much easier, and even become a plug-and-play experience. Until then, one can get portable DACs to play hi-res music with either careful choice of DAC or a little additional work, as I have described. Hopefully this post will help others who are interested in exercising all of the capabilities of their high-resolution audio devices.