• iPod Classic + iStreamer DAC + Portable Headphone Amp + High Quality Headphones: Once the iStreamer was put into the signal path, this playback system took another step up in performance, showing even better tonal balance, improved bass pitch definition and solidity, mids that sounded at once smoother yet also more transparent, and an overall presentation that was noticeably more coherent and focused.
Playing the iPod Classic through a good LOD cable and headphone amp improves its sound quality significantly and offers a good portable solution. For desktop or other in-home applications, however, adding the iStreamer elevates sound quality further still, giving a significant jump in performance, making the modest iPod sound more like a high-end source component in the process.
For this comparison I conducted two listening tests. I began by listening to lossless CD-resolution digital audio files from a Windows PC (running iTunes) connected via USB inputs to a NuForce Icon HDP, which is a combination USB DAC/headphone amplifier. Next, I changed out the digital front end of the system, playing the same lossless digital files through an iPod Classic that was connected to the iStreamer, with the iStreamer’s analog outputs driving the analog audio inputs of the NuForce Icon HDP amp. All listening was again done through Ultimate Ears In-Ear Reference Monitors.
• Computer + NuForce Icon HDP DAC/Amp + High Quality Headphones: The PC/NuForce-based system sounded very clear, but offered somewhat lighter tonal balance than would have been ideal. Relative to typical non-PC-based systems, the PC/NuForce-driven system offer better midrange focus, exceptional transient detailing, extended highs, and overall stability and coherence comparable to the results achieved with the iStreamer in the system.
• iPod Classic + iStreamer DAC+ NuForce Icon HDP Amp + High Quality Headphones: The iPod/iStreamer/ NuForce-based system offered slightly warmer and more full-bodied tonal balance than the PC-based system did, with superior bass weight, midrange focus that was good (though perhaps not quite up to the Icon’s level of performance), good transient detailing and smooth highs, and with just a trace of treble rolloff.
Both the PC-based and iPod/iStreamer-based desktop systems offered better sound quality that could be achieved using just the analog outputs of an iPod as the “front end” of the system. Which digital source one prefers—the PC + NuForce DAC vs. the iPod Classic + iStreamer DAC—largely will be a matter of listening tastes. The PC + NuForce DAC combo will appeal to those who prize clarity, transient speed, and treble extension, though its sound might be too lightly balanced for some tastes. The iPod Classic + iStreamer DAC combo, on the other hand, will appeal to those who favor a smoother, more relaxed, and more organic sound, while giving up only a subtle degree of apparent transient speed and definition. The iPod + iStreamer combo’s superior bass performance and warmer tonal balance will, I think, strike many listeners as offering the more forgiving and “musical” sound overall.
For this comparison I conducted two tests. First, I played a group of Redbook CDs through a very high quality, high-end Musical Fidelity kW SACD/CD player, which in turn was connected to a hand-made Burson Audio AB-160 vacuum tube buffer and HA-160 headphone amplifier. Next, I played lossless CD-resolution digital audio files ripped from those same CDs through the iPod Classic/iStreamer DAC combo, which also was connected to the Burson Audio tube buffer and amp. All listening was done through a pair of HiFiMAN HE-5LE planar magnetic headphones.
• High-End Disk Player, Headphone Amp and Headphones: Not too surprisingly, the multi-thousand dollar Musical Fidelity kW SACD/CD player delivered higher performance in an absolute sense than the iPod/iStreamer combination did. The big Musical Fidelity player’s sonic superiority manifested itself in several ways; the kW player offered a heightened sense of transparency and openness from top to bottom, greater treble clarity and extension, a subtle quality of harmonic richness and self-consistency, and a quality of dynamic energy and “jump”—particularly on syncopated pop music. But with all of this said, the fact is that the iPod/iStreamer combo came closer (much closer) to the sound quality of the benchmark player than it had any right to for the money.