Better Sound Quality From Computer And The Need For A Good Headphone Amplifier
(DAC and Headphone Amp User Guide)

Introduction

CD-ripping software is capable of reproducing “bit perfect” digital music data (16 bit/44.1kHz) from audio CD files stored on the computer’s hard drive. In addition to CD-quality music, some online sites are now offering 24 bit/96kHz music files. Thanks to larger and increasingly economical hard-disk capacity, consumers can store the highest quality music files on their computers. However, extracting good sound from the computer poses problems.
 

Poor Sound Quality

As a rule, your computer’s audio doesn’t sound quite right because manufacturers treat their products’ audio output stage as little more than a necessary evil. So long as the music signal remains in a digital format, all is well. The pitfalls begin when the computer converts signals to analog, which is how we listen to music. The onboard converter (a.k.a. sound card) is typically a low-cost item. Digital circuitry generates noise that often bleeds into the audio stage. Further, these compromised stages are seldom designed for the low-impedance power high-quality headphones require. Finally, should you use the computer’s software to reduce volume, you may actually be listening to eight-bit resolution –– in real-world terms, not at all good.

In sum, these deficits conspire to produce inferior sound. Far better to send the digital signal to an external digital-to-analog converter (DAC). NuForce Desktop products employ quality DACs.
 

Digital Connections

There are two methods for extracting digital signals from your computer. The universal serial bus (USB) connection is the de-facto standard for just about all peripherals: printers, digital cameras, etc. The USB allows the computer to speedily recognize a connected device. Some computers also incorporate the Sony/Philips Digital Interconnect Format (S/PDIF), a coaxial connection with excellent transfer properties.
 

USB Audio and Performance Optimization

USB specifications define a standard interface: the USB audio-device class, which allows a software driver to work with the currently available USB sound devices. Microsoft Windows and Apple Mac provide support for USB audio devices. NuForce Desktop USB DACs convert USB digital data to the analog signal headphones and amplifiers require. Equally as important, how the USB DAC performs affects sound quality.
For more information on this subject, see http://en.wikipedia.org/wiki/Universal_Serial_Bus

Some Optimization Tips

To minimize noise and dropouts, connect your audio interface to a port at the back of your computer. Ports on the computer’s face, monitor or keyboard generally don’t perform as well.

If you use a USB hub, choose one with its own AC power adapter. In areas that produce a high level of radio or electrical interference, upgrading to a quality USB cable, i.e., one with extra shielding and a ferrite bead (the cylindrical collar on one end of the cable) to help eliminate noise. Once you’re properly connected, your computer’s operating system should automatically detect your NuForce product. From that moment on, all you need to do is enjoy!
 

Windows PC Driver Optimization

ASIO4ALL is a hardware-independent, low-latency ASIO driver for WDM audio devices that employs WDM Kernel-Streaming and other sophisticated methods.
 

What You Should NOT Do

Do not replace or tamper with your existing sound-card drivers.
Do not install any kernel-mode components that might affect your system’s stability.
Do not “over-clock” or operate your audio hardware in ways that have the potential to do harm. This will void your warranty. (In certain cases, your hardware’s manufacturer states that the use of ASIO4ALL will void your warranty.)
No software-driver optimization is required for the Apple Mac OS.
 

S/PDIF Connection

The Icon HDP permits an S/PDIF connection from your computer, if that’s your preference. For best results, use a high-quality S/PDIF cable. Once the connection is made, select S/PDIF in your System Preferences Audio Device settings.
 

Analog Connections

You need only connect headphones to your NuForce device’s headphone jack and adjust for volume with the unit’s volume control. If connecting to an external amplifier or stereo receiver, you will require a quality stereo interconnect with a standard male RCA connector for plugging into the NuForce device and an appropriate connector at the other end (usually, an RCA).

Further reading: USB Audio And Performance Optimization
 

Note on Headphone Use

Headphones present a challenge to amplifier designers. There are two basic types: the over-ear (OE) in general use in the recording industry and the smaller in-ear (IE), a.k.a. ear-bud, commonly used with portable devices such as MP3 players. Given the range of available OE and IE headphones, in attempting to deal with all of them, your computer’s headphone output is optimized for none. Your NuForce Icon product will make a world of difference.

The reason is simple enough. Various OE and IE phones cover an expanse of electrical impedances from 16 to 600 Ohms and differ in other significant way. Sensitivity is a term that expresses how loud the headphones will play at a given amount of electrical power, e.g., x number of decibels per milliwatt (0.001 watt) of power, expressed as xxxdB/mW.

Typically, OE types exhibit sensitivities of about 100dB/mW, whereas IE devices can be 10dB higher or more, e.g., 110dB/mW. Assuming a 10dB difference, the lower sensitivity OE headphones require ten times more power to achieve the same volume as the IE type. If you’re using OE headphones, you’ll appreciate the NuForce Icon Series power capability. Your headphones will sound clearer and more natural. If you use IE headphones, owing to their higher sensitivity, you may notice a small amount of background noise. Conversely, you will hear weak signals more readily than would be the case with lower-sensitivity OE types.

We are not discussing a product defect. Electrical noise arises from many factors, one of which is the amount of amplification the Icon product provides. Irrespective of type or design, electrical circuits introduce noise. If the device amplifies the signal, the noise coming into it will likewise be amplified. Further, the amount the device itself creates will also be greater. These are facts of electrical life that good design can mitigate. In the case of IE headphones, noise can be minimized or all but eliminated by reducing the amplifier’s gain. But to do that, the advantage the amp offers to OE headphone users would be sacrificed. Performance benefits for one type of product diminishes those of the other. As always, effective engineering requires compromise: the NuForce Icon Series of products represents the best possible compromise. Noise will be low in some cases, and in others, quite imperceptible. As the bottom line, OE headphone users will benefit from the power they require.
For further reading: http://www.nuforce.com/hp/support/icon-hdp-noisefloor.php