Headphones and Earphones
- Written by Chris Groppi
- Published on 23 April 2009
- Denon AH-D7000 Headphones and Headroom Ultra Desktop Headphone Amplifier
- Page 2: Design of the Denon AH-D7000 Headphones and Headroom Amplifier
- Page 3: Setup of the Denon AH-D7000 Headphones and Headroom Amplifier
- Page 4: The Sound of the Denon AH-D7000 Headphones and Headroom Amplifier
- Page 5: Measurements for the Denon AH-D7000 Headphones and Headroom Amplifier
- Page 6: Conclusions about the Denon AH-D7000 Headphones and Headroom Amplifier
- All Pages
Setup (or an aside into computer audio)
I deployed the HeadRoom/Denon pair on my desk at work, fed by my computer workstation, a AMD Athlon X2 based machine running Windows XP SP3. Little did I know the effort I would need to go through to supply a high quality digital feed to the Ultra Desktop. I would have preferred to use the USB input and iTunes as the player, but both these methods offered some serious limitations. The Ultra Desktop’s USB input can only accept a 16 bit 44.1 kHz input. As I do have some high resolution digital audio in FLAC and Apple Lossless format, I wanted to be able to feed the Ultra Desktop with a 24 bit 96 kHz signal. Most low cost soundcards do horrifying things to the digital signal, not limited to internal processing at 16 bit 48 kHz regardless of the input signal or desired output signal. I installed a M-Audio Audiophile 2496 soundcard in the PC. This is one of the least expensive soundcards that offer a fully controllable 24 bit 96 kHz digital output. It is available for less than $100. This card also is compatible with ASIO (Audio Stream Input/Output) drivers. Typically, all audio on Windows machines is processed by kmixer, the underlying audio engine in the Windows OS. While it is possible to get good performance with kmixer, it is almost impossible to tell what kmixer is doing. It may or may not perform all manner of sample rate and bit depth conversion on an audio stream without your knowledge. ASIO bypasses kmixer and sends the digital audio data directly to the audio device without any intervention. Use of ASIO requires a soundcard with an ASIO driver, which was provided with the M-Audio Audiophile 2496. For some other common soundcards, including the USB sound CODEC, a free ASIO driver called ASIO4ALL is available on the web for free download (but only supports 16 bit word size and maximum 48 kHz sample rate for USB). The audio player also needs to support ASIO output. The “industry standard” player iTunes, does not support ASIO output. I used another free player, Foobar2000, configured with several plugins to approximate iTunes functionality. While it is not as easy to use or as pleasant to the eye, it does offer ASIO output and offers the user complete control over audio output.
When used on a Macintosh computer running OS X, iTunes does not have to deal with kmixer, and does output a file’s native bit depth and sample rate in a “bit perfect” manner, as long as the digital interface can handle the data. Unfortunately, I am forced to use a Windows box at work to be able to run Windows specific software without the performance penalty of a virtual machine environment like Parallels of VMware.
With the M-Audio soundcard and Foobar2000 configured to feed the Ultra Desktop native bit depth and sample rate data through the coaxial digital input, I was able to get the performance I wanted and was confident that the system was doing what I expected.
I recently ripped all my CDs and DVD-Audio discs to Apple Lossless format and/or FLAC (Free Lossless Audio Codec). Both are capable of encoding high-resolution audio (up to 24 bit 192 kHz) in a lossless manner, i.e. the decoded data is bit identical to the source data from the disc. Lossy formats like MP3 and Ogg do not encode the data such that the decoded data is identical to the source therefore information is lost. The Apple Lossless decoder in Foobar2000 does not decode high-resolution files, only 16 bit 44.1 kHz. I therefore converted all my high-res files to FLAC. At home, I use a Mac for audio so I retained the ALC files for that use. iTunes currently does not support FLAC.
All this is proof that computer audio is not as transparent as it should be for audiophiles. This stuff should Just Work, even across platforms. It does not. It takes a bit of investment in time to learn the details to get your computer working as a high quality digital transport for your situation. When this is done, however, the results can be very good. At home I feed my main system with an Apple Airport Express wirelessly connected to my Mac. It feeds a Bel Canto DAC-1.1 with a Toslink connection. The Bel Canto does a good job of rejecting jitter from the Airport, resulting in sound that is actually superior to my Oppo DV-983H when used as a CD transport for 16 bit 44.1 kHz files. The Airport Express does not support high resolution digital files (Grrr!).
For break-in, I played my playlist from the beginning at moderate volume over a weekend while I was not in the office. These 48 hours or so of constant music did a reasonable job at breaking in the drivers. The HeadRoom amplifier was an already used show demo unit, so it required no burn in.
Links for computer audio software and information:
- Foobar 2000 audio player for windows 2000/XP/Vista
- ASIO4ALL free ASIO driver for USB audio and many common soundcards
- Make Foobar2000 Look Like iTunes
- FLAC: The Free Lossless Audio Codec
- Apple Lossless Codec
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