Product Review - Meridian 518 Digital Audio Processor - July, 1996

By Stacey Spears


Meridian 518

Meridian Audio Ltd. Meridian America Inc.
Stonehill 3800 Camp Creek Parkway
Stukeley Meadows Building 2400
Cambs Suite 112
PE18 6ED Atlanta
England GA 30331
Phone: (01480) 52114 Phone: (404) 344-7111
Fax: (01480) 459934 Fax: (404) 346-7111
Meridian 518 Inputs: 1 Digital Optical, 2 Digital Coax, and 1 shared Digital Coax / AES/EBU.

2 Channels up to 24 significant bits.

Output: 1 Digital Coax, 1 AES/EBU (2 Channels up to 24 significant bits.)
Price: $1695.00.
Weight: 10 lb.
Dimensions: 3.5"(H) x 12.7"(W) x 13.1"(D)


The Meridian 518 is a 2 channel digital audio computer. It has been designed to be used as:

  • Control Unit/Digital Preamp
  • Resolution Enhancement Processor
  • Mastering Processor

Basic operation is as follows: after the signal has been received by the 518, it is then sent directly to a "Twin Phase-Lock-Loop" which is used to de-jitter the signal. The signal is then sent to a 42Mhz DSP which performs the enhancement processing:

  • Matching input word length to output word length
  • Pre-emphasis or De-emphasis
  • Dither

When used as a preamp, all sources must be digital, and any analog sources must be first run through an A/D Converter. In my system, the 518 is used between my (digital) preamp and surround sound processor. My preamp is the Meridian 562V, which has an A/D Converter built-in. The 518 allows you to set the input word-length: 16, 18, 20, 22, and 24 bits, as well as the output word-length. My surround sound processor (Meridian 565/AC3) has the ability to accept digital input word lengths up to 24 Bits (Meridian recommends setting it for 22 Bits).

I utilized different inputs for reviewing purposes. I have one set for 22 bit, one for 16 bit input, and one bypassing the 518 totally (this required the removal of the 518 from the chain). My source for both music and film was a Pioneer Elite CLD-99 LD player. Let me explain a little about how the sources are setup inside the 518. The 518 allows 12 Virtual Sources (Only 4 physical inputs). It is possible to use all 12 sources using only 1 input! The 518 will retain the settings for each source on that one input. I setup the "CD" source with the label CD; Input 16 bits; Output 22 bits. I then setup the "RD" source with a label of CD; Input 16 bits; Output 16 bits ( "CD" and "RD" are the source buttons on the Meridian System Remote, and there are 10 others, "LP", "TV", "LD", etc.). With this ability, I could also assign various DSP and Dither settings to each mode. Setup is very flexible; imagination is "virtually" your only limit.

The 518 contains four operating modes:

  • Normal - The mode in which the 518 is performing its duties.
  • Standby - Self explanatory.
  • Type - This determines how the 518 is used (Preamp, Resolution Enhancer, or a Mastering Processor).
  • Config - Where all communication and hardware options are setup.

 All updates to the Processor are software (EPROM) based. Since I have had the unit, I have been through two software updates, and one hardware update. My first update was around December of 1995. This was both a hardware and software update. The update was required to allow AC-3 data to pass through the 518 intact (The 518 strips out the subcode). The software was Ver 1.14, which contained a new item in the Config section. The option was "Data Y/N", which meant a particular source could pass the AC-3 data. If set to "N", it would mute the source. If set to "Y", the source would pass. The other software update, Ver 1.15, contained enhancements to the User Interface (e.g., when you press either Input or Output for word length, the first time it would show the value, whereas on previous versions it would immediately change the settings). Again another new option showed up in the Config section. This time it was "CLIP Y/N", which is a feature that turns on and off the Clip indicator. I am not sure why you would want to turn off the indicator. If the signal is above full scale, I would like know!.

Like other Meridian Products, there is an RS-232 port located on the back. The instruction manual contains the proper communication settings and commands required to connect a PC to the 518. I had trouble at first because I tried to connect a standard serial cable from my PC to the 518. After becoming frustrated, I thought it was my Visual Basic program. I gave Meridian U.S. a shout, and they gave me the pin config for the 518. The pin settings on the 518 are the same as my PC, so I had to reverse the send and receive wire (i.e., a Null Modem cable for you gamers). Voila, contact was made, and I had my PC acting like their remote. While I had fun with this, I didn't find it convenient to leave my PC connected all the time. This is more suited for Crestron or other companies that supply room control systems.

The 518 contains numerous options. The unit comes with a 57 page manual that covers ALL. I have seen other people write about the difficulty of interpreting their instruction manuals. No problem here folks! I have found Meridian manuals to go in-depth covering most scenarios. While not always straightforward, it's all there in black and white (pun intended).

How it Sounded

While most owners will probably use the 518 in a music-only system, rest assured it plays an equally important role in a home theater system. For the review here, I will break the description down into two sections: Music and Film Soundtracks.


Emphasis! This is the key to great playback. I was able to use this feature on most of my CDs, not all, but most. When you add emphasis, you might have to reduce the gain. While the book says you can set gain to as much as -6, I have found that going below -4 doesn't always work for me. The 518 made bad CDs sound good, and good CDs sound great. The only trouble is that not all CDs are recorded at the same level, so when using "Emph", I had to adjust "Gain" with most CDs. Alanis Morissette required "Gain" to be set between -4 and -5, and the entire CD sounds much sweeter with the 518 inplace. The two new Sterephile CDs, "Sonata" and "Festival" required no adjusment on "Gain." These two CDs really showed off the 518's ability. Since both were mastered using the 518, it only makes since to have the 518 in playback. One of my older CDs, the soundtrack of "Young Guns II" performed by Jon Bon Jovi, came to life. Gain was set at -3. It was like someone had remasterd the CD to audiophile standards. Every CD I played was improved.


Film Soundtracks

The ability of your surround sound processor to do its best depends on the quality of the signal it receives from its source. Today's best source happens to reside in the digital domain. Most, if not all, LD players have high sources of digital timing errors (i.e. jitter), and the 518's first job is to eliminate that jitter. Another problem with LDs is that, for the longest time, it seems no one, until recently, has really followed any standard for the recording level. Since the 518 has the ability to add gain, or raise the level, this insures that you are getting the most of those 1s and 0s. I have found that "Emphasis" does not work well with music soundtracks. However, what does happen is GREATER LOW LEVEL RESOLUTION! There was a noticeable increase in ambience when the 518 was engaged. "Leaving Las Vegas" has a beautiful score, and when the 518 is engaged, the soundfield just blooms. On the 10th anniversary of Les Miserables - one LD that Emphasis worked well with - the 518 helps to recreate that live performance. While Lea Salonga, Eponine, was performing "On My Own", the 518 smoothed out her voice, removing that kinda glare that happens with a female voice. I experienced Les Miserables in my living room! In terms of the Foley, with the 518, subtle sounds were revealed as if they were just added since the last time I listened. From the opening sequence of Criterion's version of Bram Stoker's Dracula, to the arrival at the Counts castle, there are layers and layers of Foley. With the 518 running, I heard creaks and other subtle detail that I never knew existed. Another good example of subtle detail is Indiana Jones and the Temple of Doom.  Throughout the movie, I encountered more and more detail. The 518 improved everything I tried!

In Closing

The Meridian 518 Digital Audio Processor is one piece of gear that I WILL NOT LIVE WITHOUT. When I first installed the 518 in my system, I had just moved and added new front speakers. My new home's living room is WAY better than my previous domicile, and my system sounded better, accordingly. It was a couple months after I had the 518, when I removed it for the AC-3 update. I thought something was wrong with my surround processor, but nope, it was the lack of the 518. I had the same problem when I updated my laptop from a 486/75 to a Pentium 75. I really noticed no super improvement, but when I had to use someone else's 486 for a while, I wondered how I ever lived without the Pentium! I must say that the DAC used after the 518 in the chain has a big effect on the ultimate sound. I have had great results with the built-in DACs on the 565, but nothing compares to the 518 demo at HiFi 96. They were using their DSP6000s after the 518, and WOW, I heard even greater improvements. If you want to remove the "digital sound" (that unfortunate metallic sheen that is prevalent in digital recordings) out of your system, I would look no further than the 518.

Stacey Spears

Copyright 1995, 1996, 1997 Secrets of Home Theater & High Fidelity
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