Music in the Round #67
First, in listening to multichannel music, the soundfield surrounds us, just as it does in real life. In anything less than a room with very bad acousticseg, a tiled bathroomthe ear/brain can distinguish the frontal soundstage from the reverberant surround field, which allows the listener to focus attention on the former. The surround field doesn't go away, but the attention of the two-channel listener is directed toward the front; in practice, perception of the reverberant surround field can be minimized by nearfield listening or, in the extreme, headphones. However, multichannel reproduction, whether offered as an accurate representation of a real place or as a studio creation of an imagined one, demands that the signals and the tonal character of the surround field be integrated into one's perception, and therefore requires that all of this additional information not be colored in ways that impede the brain's ability to integrate them.
Second, in order to process signals in ways not demanded of two-channel products, modern digital multichannel products need digital signal processing (DSP). Right off the bat, the product's DSP decodes an increasing number of lossy and lossless audio formats, then routes the appropriate signals to an increasing number of arrangements of channels/speakers. While it's relatively easy to place two identical speakers equidistant from the listener, it's quite difficult, in anything less than a dedicated room, to place five or more identical speakers optimally and equidistant from the listener. DSP is useful for 1) adjusting time delays to compensate for different speaker distances, 2) adjusting volume levels to compensate for the sensitivities of systems comprising different speakers, and 3) introducing bass management to reroute low frequencies to the larger speakers or to a subwoofer, in recognition of the fact that many people will use smaller speakers for some channels.
This convergence of a greater role for room-acoustics treatments with the presence of DSP engines has created a perfect storm of electronic room-correction devices designed to be used as integral parts of multichannel systems. However, such facilities remain rare in two-channel electronics, where, when used at all, they are implemented as standalone components. So, despite the observation that general principles of acousticsas well as good room design, construction, and treatmentapply equally to two- and multichannel systems, multichannel devices give us more tools.
However, it seems that the general interest in room/speaker equalization is now slowly filtering down to two-channel listening. Joining such long-established products as the Z-Systems rdp-1, Rives Audio PARC, and the DEQX processor (review in progress), miniDSP (footnote 1) has announced two stereo devices that incorporate the two-channel version of the DiracLive software that I'm enjoying in my multichannel system (See "Music in the Round," May 2014). They differ in that the DDRC-22A has balanced analog inputs and outputs (XLR), while the DDRC-22D has digital (S/PDIF, TosLink optical, AES-EBU). Both can operate at resolutions and sample rates up to and including 32-bit/96kHz, and come with the necessary microphone (a UMIK-1) and Windows-compatible software for measuring and calibrating. Macs are not supported. Given the individual prices for the DiracLive software (&128#;389, $540) and the mike ($75), the DDRC-22s appear to be tremendous values at $899 each (see www.minidsp.com/products/dirac-series).
But waitminiDSP also has something new for multichannel . . .
miniDSP nanoAVR 8x8
In my January 2014 column, I told the story of my fascinating time with miniDSP's 10x10Hd digital signal processor. It has all the tools for implementing correction filters in up to 10 channels (8 analog, 2 digital), and worked as advertised. My concerns were that as it only had analog inputs and outputs, analog signals had to be passed through its onboard A/D and D/A converters, and that its internal processing was limited to 48kHz. The A/D/A conversions are redundant and could compromise the sound of a system chosen for its outstanding DACs. The 48kHz limitation is of somewhat less concern because we now know that the various softwares of the major player in room EQ, Audyssey, have been implemented in many products with a downsampling of all HD signals to 48kHz, and without great hue and cry. Still, such downsampling betrays a skimping on DSP resources that should not be tolerated in a high-end product.
Now miniDSP has produced an affordable external processor, the nanoAVR 8x8 that costs $299 and that sidesteps both issues. First, it offers something novel for an equalizer: dual HDMI inputs and an HDMI output. This means that, unlike the 10x10Hd and most other standalone multichannel equalizers, it can accept, process, and output up to eight channels without any A/D/A conversions, even as it passes the video signal through without any processing. Second, while it can accept up to 24/192 PCM and its internal handling is 32-bit, its throughput is only 24/96still, in my opinion, a significant advance over 24/48.
The nanoAVR 8x8 comes in a trim and tidy black case, has no power switch, and is intended to remain on at all times. The single button on the front allows the user to choose one of the four EQ configurations and two HDMI inputs. There is an IR receiver and LED for monitoring and remote control (not supplied). On the rear panel are three HDMI V1.4a jacks (two inputs, one output), Ethernet, and USB ports, and a power connector for the supplied wall wart. These ports are solely for control and setup (although I briefly dreamed of using the nanoAVR to insert EQ into a streaming/networked system). There are no facilities for audio measurements, and users must install the appropriate plug-in from miniDSP on their Windows or Apple computers in order to configure and upload its correction filters to the nanoAVR. Those filters can be created ad hoc or uploaded from another program, such as RoomEQ Wizard (REW).
Footnote 1: miniDSP Ltd., Unit 1204, Crown Industrial Building, 106 How Ming Street, Kwun Tong, Hong Kong. Tel: (852) 2358-2066. Web: www.minidsp.com.