Processor 101

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PLEASE NOTE - This needs to be updated following the release of the HD621 and 861v6

First of all, well done! If you're looking for the best in multi-channel digital audio processing, then you're looking in the right place: Meridian Audio produces quite brilliant domestic multi-channel audio processors (Bob Stuart et al. invented them, in fact).

So you're interested in buying a Meridian multi-channel audio processor, but don't know where to start? What are your options? Which model? New or second-hand? These are not easy decisions to make, particularly if you are looking to step on to the Meridian ladder for the first time with limited funds (which many many Hikers have done before you). This primer should help; if you still have questions after reading it, please ask them in the main forum; _somebody_ will know the answer.

Note the following key to ballpark cost:

$$$$$ $20,000
$$$$ $10,000
$$$ $5,000
$$ $2,000
$ $1,000


Let's get this of the way first. Meridian believes that allowing HDMI into a processor has a detrimental effect on sound quality. See the bottom section of [this long post |] (under the heading "HDMI") for comments from Bob Stuart on the subject. As long as they continue to hold this position, there will never be a Meridian processor with built-in HDMI intputs. Instead, they have chosen to use an external device to extract audio from the HDMI without the HDMI having to go into the processor: this box is the HD621. It also has HDMI switching functions (and other capabilities) and replaces the HDMax421, which was only an HDMI switcher which could be integrated into the Meridian COMMS system.

The HD621 outputs audio via 4x SPDIF or MMHR (8 channels over Cat-5 cable) using PCM or MHR, and also allowing SmartLink metadata to be passed to the processor (indicating info about the source). The only Meridian processor that can accept 7.1 from the HD621 is the 861v6; the 861v4, 861v3, all G68 variants, all G61 variants and the 568.2MM will accept 5.1 from the HD621.

Note that it is also possible to modify suitable HD DVD, Blu-Ray, SACD, and non-Meridian DVD-Audio players so that they can pass multi-channel PCM to a Meridian processor, but this is beyond the scope of this primer. There are other possibilities, such as [this |].

Current processors (wot u can buy new)

861v4 ($$$$$)

The 861v4 is Meridian's reference processor. It is a modular design and, although it is sold in _Analogue Theatre_ and _Digital Theatre_ configurations, it is usually purchased in a custom configuration depending on the customer's specific source components and speakers. If you need a multi-channel analogue input, you add a card. If you need balanced analogue outputs, you add a card. Etc. Complete flexibility. Very expensive.

It features a DSP core capable of 750 MIPS (million instructions per second). Headline features include FIFO de-jittering of all digital inputs, upsampling of multi-channel PCM inputs (e.g. from a Meridian DVD player), proprietry decoding of Dolby Digital and DTS bitstreams, sophisticated DSP soundfield manipulation (DSP presets for stereo and multi-channel material), and Meridian Room Correction (MRC).

To date, there have been four incarnations of the 861. Historically, upgrades have been offered to bring the original 861 up to 861v2, 861v3, and 861v4 spec. On the Hitchhikers forum there is an _expectation_ that 861 development will continue and further upgrades will be offered, but although this is likely it is not guaranteed as Meridian does not publish its development roadmaps. The next major upgrade is expected to involve an HDMI v1.3a input card (or equivalent solution) and associated internal software changes (e.g. to accommodate 7.1 input channels). No timescale for such an upgrade has been announced.

  • Note:* The 861 does not have the processing power to decode a Dolby Digital (DD) or DTS bitstream _and_ upsample the channels. To gain the benefits of upsampling DD or DTS soundtracks, a Meridian DVD player (or other suitable modified player) must be used to decode the bitstream and pass multi-channel PCM to the processor.
Variant Output Channels Features
Digital Balanced Unbalanced Room Correction Video Switching AM/FM Tuner Multi Zone
861v4 Custom Custom Custom Yes No No 2 (with TP00 card)

G68 ($$$$)

The G68 is the poor man's 861v4! Joking aside, the G68 offers much, and in some systems probably all, of the 861 at half the price: The G68 shares the same 750 MIPS DSP core and processing algorithms as the 861. In an _all digital_ system (digital sources, Meridian DSP speakers), arguably, you would not notice a difference between the G68 and 861. YMMV. What you sacrifice is the ultimate in performance on the analogue side, flexibility, and future-proofing. Having said that, internally, the G68 is a clean card-based design which should lend itself to upgrading.

On the input side, all G68s have two multi-channel 5.1 digital inputs and two multi-channel 5.1 analogue inputs (with very high quality analogue to 96/24 digital conversion using the same ADC chip as the latest 861 IA45 card). There are plenty of stereo digital coax, optical, and analogue inputs as well. The type and number of outputs vary according to the particular variant, as do the peripheral features such as analogue video switching, tuner, and multi-zone capabilities. See the table below for a comparison of the different variants.

Current G68 Variants

Variant Output Channels Features
Digital Balanced Unbalanced Room Correction Video Switching AM/FM Tuner Multi Zone
ADV 10 None 8 Yes Yes Yes 3
AXV None 4 6 Yes Yes Yes 3
XXV None 8 None Yes Yes Yes 3
AXD 10 4 8 Yes Component Yes 3
XXD 10 8 2 Yes Component Yes 3

ADV, AXV and XXV The latest incarnations of these variants have a USB input instead of the O1 optical input on older models; there are still four optical inputs. It is hoped, but not guaranteed, that an upgrade will be offered to owners of original spec xxV variants. The following caveat on the latest G68 spec sheet is not encouraging though, although it may simply be a disclaimer:

_Meridian Audio reserves the right to amend product specifications at any time and *we cannot guarantee that older models can be altered to conform to later specifications*._

The "V" moniker refers to analogue video _switching_, but beware that there are limitations to this functionality (e.g. component switching is limited to 1080i and the only format conversion is from s-video to composite on the _zone_ outputs).

AXD and XXD (USA only) These are brand new variants for the USA market only. They are similar to the original AXV and XXV variants, but gain 10 digital output channels at the expense of composite and s-video switching. Switching of component video is retained.

Note: The G68D and G68J variants are no longer current models (see below).

The latest spec sheet is on Meridian's media site:

G61R and C61R ($$$+)

The G61R is essentially a G68ADV in a smaller physical package, but without analogue video switching, tuner, and multi-zone outputs. Its inputs are identical to the current G68 models (with USB input) and its main outputs are identical to the G68ADV. The DSP code appears _identical_ to the G68 (and 861 for that matter). The G61R has identical processing power to the G68 and 861 (confirmed in the CES 2009 Q&A session).

  • IMPORTANT!* Do not confuse the G61R with the short-lived G61. The G61R is current; the G61 is not. The G61R has MRC; the G61 does not. It is _very_ unlikely that an upgrade will be offered.

The C61R is a G61R in an installer friendly case.

Variant Output Channels Features
Digital Balanced Unbalanced Room Correction Video Switching AM/FM Tuner Multi Zone
G61R 10 None 8 Yes No No No

Older processors (ex-dem and s/hand only)

Of the processors below, only the G68 (all variants), G61 (all variants) and 568.2MM can accept multichannel PCM input from HDMI via an HD621.

Although the HD621 can output 7.1 if the software contains it, and these processors can output 7.1 to speakers, this does not mean that the two together will be a discrete 7.1 system. The G68, G61 and 568.2MM cannot accept a 7.1 input, and so the HD621 will instruct the source to downmix to 5.1; these processors are then able to matrix 7.1 out of the 5.1, but this is not the same as the 7.1 from the BD getting to your speakers. How big the difference is will depend on the software and the system as a whole. Your Mileage May Vary.

The 861v6 is currently the only processor able to accept 7.1 channels from the HD621, and thus the only Meridian processor able to be a part of a discrete 7.1 system.

861 / 861v2 / 861v3 ($$+ to $$$$) To be written.

G68D / G68J ($$$)

Variant Output Channels Features
Digital Balanced Unbalanced Room Correction Video Switching AM/FM Tuner Multi Zone
D 10 None 2 Yes No Yes 3
J(apan) 10 None 8 Yes No No No

The G68J was developed with the Japanese market in mind, but appears to have become a very popular variant. It is essentially a G68ADV without video switching, tuner, and zone capabilities, so it would work very nicely with a G91 (which itself has a tuner). Note that all G68s since the introduction of the "J" also have AAC hardware decoding on the main board. AAC is big in Japan, apparently... G68s prior to the introduction of the "J" do not.

G61 / C61 ($$$)

Variant Output Channels Features
Digital Balanced Unbalanced Room Correction Video Switching AM/FM Tuner Multi Zone
G61 10 None 8 No No No No

The C61 is a G61 in an installer friendly case.

  • IMPORTANT!* The G61 does not have Meridian Room Correction. It is _very_ unlikely that an upgrade to the G61R will be offered.

568 ($) / 568.2 and 568.2MM ($$)

The 568.2MM is the cheapest Meridian processor to accept multichannel PCM input. Through the connection of an HD621 it can accept multichannel loss-less hi-resolution audio from HDMI: this could be from BD or from SACD/DVD-A according to the capabilities of the transport in question.

Approx £500 for a vanilla 568. This is an incredible bargain.

More details to follow.

561 ($)

Approx £500 for a vanilla 561. This is an incredible bargain, but nothing compared to the vanilla 568 which is now going for the same money. It's a mad mad world...
More details to follow.

565 ($)

The Meridian 565 is the one that started it all; and when I say all, I mean home theatre. Yes, really. The 565 was replaced by the 568.

As with subsequent Meridian processors, there were both software and hardware upgrades and you want to have one with the "Z3" card installed (see below). It has limited connectivity (1x optical, 1x SPDIF and 1x analog) so it needs a 518 or 562 to add inputs. There are no multi-channel inputs here (digital or analogue) and absolutely no prospect of them either!

  • The latest firmware is 565 Z3 6.2a.
  • Firmware v6.0 is ok if you don't have a Meridian DVD Player.
  • The Z3 is a Meridian 7.1 version with DD and DTS where 7.1 channels are derived from 5.1 bitstream inputs.
  • The digital inputs accept 24-bit PCM and DD/DTS bitstreams.
  • The digital outputs are limited to 22-bits. (Compatibility issues with 96/24 speakers? TBC).
  • £300 in the current climate is a good deal. Unless you are really strapped for cash, the 561 and original 568 should probably be considered the Meridian processor entry points.