With the ever increasing power and decreasing cost of electronic components we have recently entered into world where practical DSP (digital signal processing) is now possible for the average consumer. There exist a multitude of solutions available to integrate into your 2 channel or multi-channel home theater system to greatly help certain audio issues. You can now add parametric eq, graphic eq, time delay, crossover control, and many other features for as little as $80. Stepping up you can add full multi-channel digital room correction for no more then $1000; an area that until recently was limited to components over $5000. Here we will take a look at some of the solutions available on the market today, and their advantages.
MiniDSP is a well known digital signal processor manufacturer that is becoming increasingly popular as a budget, yet quite good, solution. They have a few different products that vary from $80 to $1000 and serve different needs.
MiniDSP 2×4 $105: The basic unit that made MiniDSP famous. 2 channel input, 4 channel output. Can be used to create a 4 way active loudspeaker, stereo 2 way active loudspeaker, 2.1 or 2.2 channel stereo systems (adding in 2 subwoofer channels) or a variety of other combinations including just adding EQ to your existing system. It has RCA inputs and outputs and sits in the signal path before the amplifier. It had 6 parametric EQ filters on each input and each output. Benefits are ease of use, flexibility, and cost. Drawbacks are lack of any phase control, FIR or IIR filters, and any automatic room correction.
MiniDSP 10×10 HD $599: A 10 input, 10 output version of MiniDSP. Great to put between your pre amp and amplifiers in a 7.2 channel system. The additional channels add a multitude of additional configurations. The miniDSP 10×10 HD could be used to build a stereo active 4 way loud speaker with dual subwoofers, for example. Otherwise has the same advantages and drawbacks of its smaller cousin.
NanoAVR Series $250 to $320: The NanoAVR is part of the home theater series from MiniDSP. They are a series of HDMI audio processors designed for home theater audio correction. The NanoAVR has 2 HDMI inputs and one output. The NanoAVR HDA adds 8 Analog RCA outputs. The NanoAVR HDA is a great way to add 8 channel pre-outs to a receiver without any. Both units are 24 bit 192 kHz units and support IIR filtering. The units also feature advanced bass management and 10 parametric eq filters per channel. The major drawback is the audio over HDMI must be linear PCM, so your source unit must support decoding Dolby or DTS to Linear PCM. If this is the case, then the NanoAVR units are a great choice.
OpenDRC Series, $325 to $350: The openDRC series is a number of two channel audio processors built on the same architecture as the NanoAVR series; or more specifically, NanoAVR is built based on the OpenDRC series, which came first. The four units are either, XLR in to XLR out, Digital in to Digital out, Digital to XLR stereo, or Digital to 8 channel RCA. They provide the same processing abilities as the nano avr, but are primarily designed for two channel listening. The upgrade to OpenDRC from MiniDSP 2×4 is additional parametric EQ and IIR filtering.
Audyssey is probably the most widely distributed DSP package, as it’s been included in almost all receivers made by Onkyo, Denon, Marantz and Integra for the last 5 years. It is not purchasable as a separate device, but instead is a software package that manufacturers can licence to use in their products. Audyssey is designed to work automatically with an included set up microphone to set up speaker distances, levels, crossover points (for bass management) and add digital room correction. Audyssey works in both the frequency and time domain and the higher end versions of the package work extremely well. If buying a receiver today, you would do very well to purchase one with one of the better flavours of Audyssey.
Although the specifics on Audyssey are proprietary, they have published a good amount of information on it. All flavours of Audyssey measure the room the exact same way apply the same bass management, level correction and distance correction. Where they differ is in how many filters they apply to the subwoofer and speaker (Satellite) channels and how many measurement points are used.
2EQ: Basic room correction with no correction for the subwoofer channel. Approximately 20 filters for the satellite channels. Not recommended as it has been shown that filters for the subwoofer channel are much more beneficial for home theater then satellite filtering.
MultEQ: Double the number of satellite filters, and 128x more filtering for the subwoofer channel. Recommended as the minimum useful Audyssey level.
MultEQ XT: 16x the number of satellite filters as 2eq, and the same subwoofer filters as MultEq. A good step up from MultEQ.
MultEQ XT32: 512x more filters then 2eq and 512x more Subwoofer filters. Highly recommended. Holds itself with the best of the best room correction packages on the market.
MultEQ XT32 (Pro): A special version of XT32 that requires a pro license and special equipment. Same final processing filters, but adds more measurement points and user control over the process.
Dirac Live started life as a software package designed to fix audio coming from your PC. It immediately gained huge praise, but its limited application left it as a niche product. In the last few years companies have started adding it to their products that allow Dirac Live to work for normal Stereo and Home Theater systems. The products differ, but the software process remains the same. Like Audyssey it’s a proprietary system but they do reveal a little about the system. Dirac works by measuring your room at multiple points and intelligently deciding what it can, and cannot fix, and then applies IIR filters to correct both frequency and phase (impulse) The filter resolution is extremely high, which is why it originally existed only on PC’s. You get very high level of control over the target curve that Dirac attempts to correct to. Dirac Live and Audyssey MultEQ XT 32 are nearly identical in how well they work; but Dirac is vastly superior to all lower levels of Audyssey.
So how do you get Dirac Live into your stereo or home theater system? Right now there are only a few options:
Software $550 to $950: Stereo and Multi-channel software for your PC. Must use PC as audio source. Great for home office systems; not very practical otherwise.
Emotiva XMC-1 $2500: A full featured high end per amp with XLR outputs. Comes with full version of Dirac for $100 more ($1000 value).
MiniDSP Dirac Live series $500 to $1000: Built on the OpenDRC platform, there are many versions of DL from Minidsp to suit your requirements. Two channel or Multi-channel, Digital or Analog, you can find a version to suit your needs.