For most of the 1990s and much of the 2000s, audio was essentially a video peripheral: an add-on to big-screen TVs so that viewers could have surround sound accompanying their widescreen pictures. But over the last few years, something remarkable has happened a little below the surface.

Two-channel audio, primarily for music, has made a comeback. For the most part, it's a different kind of two-channel than we had in the heyday of stereo. Today's systems are intended for playing digital music files from a portable player (not always an iDevice though) or computer. These can be portable systems for listening through headphones, home systems for serious headphone listening, or home systems for two-channel speaker playback. Some of the components are familiar (speakers, headphones), others more new-fangled (DAC, head amp).

At CES, many audio brands launched products for the burgeoning digital audio market. Some of these were from relatively new companies, others from established brands. Some were audiophile-oriented, others were aimed squarely at the mainstream.

What's interesting is how active this segment is. While still a solid category, home theatre appears to be in a holding pattern. Several companies for whom AV receivers are a mainstay - D&M and Yamaha for instance - passed on CES; and Pioneer was there only with 12-volt product. But in two-channel music, there's all kinds of stuff going on.

Scott Campbell, Managing Director of Arcam, and Kevin Main, Sales Manager at Erikson Consumer, at Arcam's CES 2012 exhibit, where the U.K. company introduced five new DACs.

Electronics

At its booth in the Venetian, Arcam launched five new DACs (digital-to-analog converters). While each addresses a specific niche, they perform a common function: they accept a digital audio stream from the source component (music player, computer), then convert it to an analog signal that can be routed to an external amplifier or powered speakers.

Doing D-to-A conversion in an external device has many advantages. The DAC chips and associated circuitry are almost invariably of much higher quality than those inside the computer or portable player. (One exception is computers with audiophile-grade sound cards.) Moving analog circuitry away from the electronically noisy interior of a digital device can pay enormous sonic dividends.

Due to ship in Canada in February for $319, Arcam's drDock is a remote-controlled dock that accepts iPods, iPhones and even iPads. Unlike many docks, the drDock accepts a digital stream from the docked device, rather than analog; so that the drDock is handling digital-to-analog conversion. In addition to analog line-level audio outputs, the drDock has an HDMI output for sending video to a connected HDTV. There's also a USB port, for connecting the rDock to a PC or Mac, for synching and charging the connected device. (For some reason, it won't charge an iPad from a PC.)

The rPAC is designed to work with Windows PCs and Macs. Connect it to a USB port on the host computer, and change the settings in Control Panel (Windows) or System Preferences (Mac), telling the computer to route audio to the rPAC instead of the internal sound card. No driver software is required. The rPAC's USB 2.0 connection is asynchronous, meaning that timing of the digital signal is controlled by the rPAC's internal clock, rather than the PC's; and that means drastically reduced jitter (timing errors in the digital stream). It supports 44.1, 48, 88.2 and 96kHz sampling rates, and bit depths of 16 and 24 bits; CD-quality and high-resolution streams in other words. The rPAC is powered via USB, so there's no external wall wart. It has an internal headphone amp, as well as RCA line-level outputs for connection to an external amplifier or powered speakers. It arrives in Canada next month for $259.

Rather than USB input, the rLink DAC has optical and coaxial SPDIF (digital audio) inputs. It can be used to upgrade the sound quality of CD players, media players and game consoles with digital audio outputs. If your computer has a digital audio out (the headphone jacks on many Macs double as optical digital outputs when used with an appropriate cable), you can use the rLink DAC for computer audio as well. It has line-level RCA analog outputs for connection to an amplifier or powered speakers. The rLink DSC will launch in Canada this March for $259.

Designed to work with PCs and Macs, Arcam's rPAC can receive digital streams with resolution to 96kHz/24 bits over its USB port. It's also powered via USB.

At CES, NAD introduced three new Masters Series components: the M50 Digital Music Player, M52 Digital Vault, and M51 Direct Digital DAC.

The rBlink Bluetooth DAC is intended for Bluetooth devices. Pair it with a smartphone or tablet, and it will receive digital audio signals wirelessly, and then output line-level analog audio through its RCA stereo jacks. The rBlink supports APT-X, for optimum-quality streaming from compatible Bluetooth devices. It ships in Canada in April for $259.

Arcam's no-holds-barred DAC is the FMJ D33 Digital to Analogue Converter. Priced at $3,299 and arriving this month, the D33 has a full suite of input jacks, including asynchronous USB, dual coaxial and digital audio, and professional AES/EBU connectors. It employs dual audiophile-grade 192kHz/24-bit Burr-Brown DAC ICs, for support of ultra-high-resolution digital music files. Other refinements include twin toroidal power transformers, premium four-layer circuit boards, and a heavy resonance-free chassis.

NAD already has several digital audio products, notably the Masters Series M2 Digital Direct Amplifier. At CES, NAD added three Masters Series audio components. The M50 Digital Music Player has a CD/DVD transport and built-in Wi-Fi networking. It can stream music off computers or NAS drives on the local network, and from storage devices connected to its USB input. It can play CDs and DVDs, and also rip CDs. Supported formats include FLAC Lossless, MP3, AAC, WMA, Ogg Vorbis, and linear PCM to 192kHz/24-bit. The M50 will be available in March for $2,500.

Users can store ripped files on the M50 on networked and USB devices, or on the companion M52 Digital Music Vault. The latter component contains three two-terabyte hard drives in RAID 5 configuration, optimized for both performance and redundancy. The drives are low-noise units designed for media, and the component itself is fanless, for quiet operation. The M52 also arrives in March, at $2,200.

Playback on the M50 and M52 can be controlled by very nice iPad and iPhone apps, which controls the Masters Series components over a local network. The app will integrate music from multiple sources (Music Vault, NAS, computer etc.) under a single interface.

The M51 Direct Digital DAC is already shipping, for $2,000. Along with optical and coaxial digital-audio inputs, it has a USB input that conforms to the USB Audio Class 2 specification, indicating its ability to support 192kHz/24-bit content. (NAD's current M2 Direct Digital Amplifier lacks USB connectivity, which is becoming increasingly important in digital audio.) There are also balanced and single-ended analog inputs, plus two HDMI inputs and an HDMI output. A two-channel device, the M51 does not do surround-sound processing. But via HDMI, it will capture and process two-channel audio from DVDs and Blu-ray Discs, and pass video (including 3D) to a connected monitor. Incoming audio from all sources is converted to an 844kHz pulse-width-modulation (PWM) stream. Volume is controlled in the digital domain, with 35-bit precision. Even with high-resolution 24-bit content, volume can be reduced to -66dB before any bits are truncated.

At its exhibit, Peachtree Audio demonstrated the new novaPre preamp and Peachtree 220 power amp playing files from a MacBook Pro.