Technical Articles and Editorials
- Written by Staff
- Published on 30 November 2007
The Secrets DVD Benchmark has been remarkably popular, but in an of itself not all that remarkable or unexpected. What took us off guard is that it has been equally popular with our readers and manufacturers of the equipment.
Stacey Spears and Don Munsil were able to, in incontrovertible terms, put down on paper exactly what should be coming out of the video jack on all our DVD players. While technically complex, in concept we just want players that read the data and do what the heck they are supposed to do with it. It's that simple.
With that in mind, our Editor-in-Chief asked the Editorial Staff to think about how we could have similar Benchmark Specifications for the other components of Home Theater. The SSP Benchmark Specifications are for dedicated SSPs (Processor/Preamps) and Surround Sound Receivers, which include SSPs.
We came to the conclusion that at this time at least, a score based system like what we have for DVD Players would be poorly received. One reason is that we can't put a number on "sound quality". We can quantify measured sound, and score on the accuracy of the representation of the signal in terms of frequency response and THD, but many still feel the subjective word "Good" is unaccounted for. Also, we are tired of the esoteric market using "good sound" as an excuse for shortcomings in usability and functionality. We've actually witnessed a manufacturer telling their customers that their multi-thousand dollar SSP does not do such and such because, "We wanted to focus on the sound quality".
We put our heads together, looked at the catalog of SSPs on the market today and in the past, and came up with an entirely reasonable and doable set of functionality criteria. While any SSP at any price should have the full repertoire of what is out there in terms of surround sound formats and CODECS, this is not about "features". Those things can affect price, some greatly so, and not everyone is in the same market price-wise. Not everyone needs or wants 15 stereo inputs, 5 component video lines, multiple RS-232 ports, balanced I/O, or a remote control that can make popcorn. What follows does not really cost money in the empirical sense. Digital audio manipulation and system control are at a point where what we want in terms of how the product functions can just as easily be done in a $500 AV Receiver as in a $10,000 SSP.
So, here are the particulars we feel an SSP should be able to meet, regardless of price:
Global AV Delay (a.k.a. "Lip Sync" Delay)
While this has always been an issue for people with certain high end video processors, more and more of the current progressive scan TVs, and all of the Plasmas, LCDs etc, are digitally processing the video signal and in most cases delaying it to one extent or another. As such, an SSP's ability to delay the audio program by a complimentary amount is becoming a must-have. We pass a unit here if it offers a global audio delay for purpose of synching the audio program with a video program delayed by a video processor. Minimum acceptable range is 0-60ms. 0-100ms or more is preferred. While a minimum acceptable adjustment increments is 15ms, which corresponds to 1 video field in NTSC, 1ms is greatly preferred. While we'd like to see this setting be unique for each input, at this time we will not fault a design for having only one global setting.
Speakers Delay, or Time Alignment is critical to getting the best performance from any multi-channel setup. We have an article on why that is so. Setting it correctly can be daunting, especially for someone new to the Home Theater hobby. We've seen some of the most expensive (and undeservedly praised) SSPs get this completely wrong. The preferred method for setting speaker delay is by inputting the distance from the prime seat to each speaker. Adjustment increments should be no more than 0.5 feet (which corresponds to 0.5ms). Each speaker in the 5.1 or 7.1 array, including the subwoofer, should be set separately to pass this test. Borderline pass will be given to units which at least keep the following groups separate: Front L/R, C, Surr L/R, and Rear L/R (it is unacceptable if Surround and Rear are lumped together, or if the subwoofer is not time aligned at all). If a unit uses "raw" ms delay for time alignment, it must automatically and transparently add 15ms to the surrounds for all matrix decode processes (fail if unit requires user to set total delay for each surround mode). Units which offer an "automatic" delay (and level) setup function with a microphone get a particular nod of approval, but these must offer a way to override and set it manually. I've had a couple manufacturers complain to me about this, saying that their mic system is accurate enough that they don't need a manual option. They shut up when I asked them what an owner is supposed to do if they lose or damage their microphone.
Some people like "Mute" to be a total silence. Others like it to be an attenuation. With most SSPs using digitally controlled analog volume, offering the choice should be a matter of course. The test unit will pass if it offers a choice of attenuation (range of choice should be -10 to -50dB with 10dB increments) or full mute. Mute must be a dedicated button on the remote.
Power On-Volume/Max Volume
These are "safety" items. It's too easy for the volume to be ramped up without due regard for where it's at. We pass the unit if it offers the option of a pre-set power-on volume. In the case of multi-zone units, power-on volume should be independent for each zone. The Unit also must offer a max volume setting or other suitable limiter, preferable if it is password protected (so the kids can't change it and blow up your speakers).
Input Level Trim
The unit must offer separate input level trim for each input.
Volume Scale and Speaker Calibration Level
The Volume scale should be industry standard relative. That is, "0dB" corresponding to reference level and descending from there in relative dB, down to (-) infinity. For the volume scale to be properly calibrated, each speaker, including front left/right, must have its own calibration setting.
Headphones should be able to monitor ant souse independent of the main zone and have their own volume control. For multi-zone units, the headphone jack must be able to monitor any zone.
DRC (Dynamic Range Control)
The unit must offer a minimum of two levels of Dynamic Range Control in addition to none or off. For a full pass, the DRC setting must be adjustable from the remote control and not be buried deep within setup menus (if it takes more than three button presses to get to it, that's too many). We also want to see a small indicator on the front panel when DRC is set to anything but "off".
Dolby Digital EX
Full pass will be given to THX Surround EX or Dolby Digital EX licensed products which use two speakers and/or line outputs for the center surround (in other words "6.1" is not acceptable). All 7.1 SSPs must respond to the EX flag in the bitstream. If not a Dolby/THX licensee (ie: "EX Clone") we test the unit for a Stereo3 matrix decoder and pass the unit only if it uses one (if a clone uses a standard matrix decoder, any out of phase material in the two surround channels will be lost).
The unit must assert Dialog Normalization and NOT provide any means for the user to defeat or bypass it. We want SSPs to have some means of indicating the current dialnorm value, ideally something persistent.
The unit should not impose any noticeable delay in locking on to a new AC-3 bitstream.
The unit must be able to play 640kbps Dolby Digital bit streams (note: 640kbps AC-3 is not actually in the DVD-Video spec but all consumer decoders should be capable of decoding it).
Surr Encode Flag Reading
The unit should read the "Surround Encoded" flag in two-channel AC-3 bitstreams and set Pro Logic/Stereo playback appropriately, and the user must be able to override.
Pro Logic II
Non-mandatory Music Features
Panorama, Width, and Dimension must be adjustable by the user to pass this criterion.
The crossover frequency of the units bass management should be selectable from at least 40 to 120Hz in at least 10Hz increments. We also want to see a choice of (A) 4th order low pass/2nd high pass (for use with THX and other dedicated satellite speakers) ,or (B) 4th order low pass/4th order high pass (for use with "full range" speakers or those not expressly designed to be high passed).
While its certainly possible and acceptable for units to offer more complex bass management options, such as a different choice for each speaker, we don't require it. In our article Miscellaneous Ramblings on Subwoofer Crossover Frequencies, we make a pretty good case for setting speakers as "small" (regardless of actual physical size) and selecting a crossover frequency at or near 80 Hz. Again, to be clear, it's not that we fault more extensive flexibility here, it's that we don't require it for our definition of correct and acceptable bass management.
Units must provide an independent LFE trim adjustment for Dolby Digital, DTS, and (in the future) MLP.
Bass Management/Time Alignment
Test units must provide an option to digitize analog 5.1 inputs so that they inherit the bass management and time alignment of the SSP. Until a digital link is standardized, this is the only way to get the most out of 5.1 music.
THX Select, Ultra, and Ultra2 Certification
Don't worry, we would not dare suggest that all units must be THX Certified to meet Secrets Benchmark. Yet because certification requires that a manufacturer design into the product electrical specs which (from what we've been able to weasel out of people on the inside) meets or exceeds anything we've thought about putting on paper, we like to see it covered. Such qualities can and most certainly do exist in non-THX SSPs but but with THX Select now appearing on AV Receivers as inexpensive as $700 SRP, the argument that the THX logo ads appreciable cost is no longer holding true.
All THX units must provide the ability to select THX Re-Equalization independent of THX Home Cinema, THX Surround EX, and THX Ultra2 Cinema. This choice should not be reset when changing modes or cycling power.
Parametric Subwoofer Eq
Units must provide a 1-3 band parametric Eq for the subwoofer output. We will accept designs which only allow a cut (and not any boost).
Surround Mode Pre-Set
Units must provide a set of surround mode preferences for each signal type, and these presets must be unique to each input. Borderline pass if it is a global set.
Multiple Surround Management
In the case of 7.1 units, a choice must be provided of where to route the surrounds of 5.1, i.e., to the Surrounds, Rears, or Both. This choice must apply to all sources, including the 5.1 analog input(s).
Academy Mono Filter
The test unit passes if it offers industry standard Academy filter option on mono playback. Borderline pass if the unit offers "clone" HF roll-off for academy mono soundtracks.
All 5.1 AC-3, DTS, and 5.1 analog inputs must be down-mixed for headphone, rec path, or stereo zone outputs. The LFE channel should be discarded from the down-mix.
Front Panel Dim
Because SSPs and AV Receivers are frequently in the front of the rooms, often very close to the TV, we feel it is of great importance that the front panel and corresponding lights be dimmable so as not to distract from the movie. Units must provide the option to dim the front panel, including all lights/LEDs, for a pass here. Preferably two illumination levels should be available, one high intensity during interaction and one low intensity during inactivity. The lowest setting available should be barely visible in a pitch black room.
Units must store (retain) all parameters (speaker level, distance, volume preferences etc.) in memory during power outage.
Notes on User Interface
While we would be delighted to see manufacturers solicit our input on SSP User Interface, at this time we are not going to spec a utopian definition of one because quite frankly, people's opinions differ here. We will however come down hard on an SSP when something is obviously wrong or universally difficult to work with.
As a general outline, we'd like to see several logical menus:
- A) Hardware setup, which would include speaker selection, level calibration, time alignment, etc.
- B) Preferences, which would include volume control options, surround mode parameters, front panel dimming, etc.
- C) Input setup, unique to each input, which would set input specific items such as level trim and surround mode presets.
ANY item which might be toyed with during normal use, such as the DRC settings, or Pro Logic II music parameters, must be readily available from the remote, and when changed during playback, must be changed in that input's setup and be retained as such. In addition, if at any point we feel we need to hook up a TV/monitor to get a handle on things, that's no good. Everything should be "doable" with the front panel display.
We will publish a separate subset to this document which defines what we want to see in terms of IR code sets in an SSP.
Like the overall UI, we are not going to dictate one perfect remote design, because there is no such thing. This is why products like the Pronto have flourished: You take a blank touch screen and turn it into YOUR ideal remote. We do however want to see certain remote control features as mentioned above. That includes quick, easy access to frequently used functions, and an overall adherence to good ergonomic design. The remote should have backlighting for use in dark home theaters, buttons appropriately positioned, and above all different in shape and size from one another, according to their function.
There you have it: Our definition of good SSP functionality as of November, 2003. We know of at least one mid-priced SSP that gets just about 100% of the above right, and several $1,000 AV Receivers which come close, so we know we're not out to lunch or unreasonable. At the same time this document is subject to update and becoming more demanding as DSP and memory further come down in price. For example, as soon as we are satisfied it can be done correctly with negligible cost addition, we will want to see EQ on all channels, most likely parametric EQ for the sub, 1/3 octave full range EQ for each front channel, and full octave EQ for each surround. To do this right will require the SSP to have its own on-board 1/12th octave or better RTA, something which today costs thousands of dollars, but which tomorrow may be on a $5 DSP chip.
You'll see our reviews of SSP products, both AV Receivers and dedicated processor/preamps, become more consistent and streamlined as we look at them vis-à-vis the above criteria, while still retaining the individual writer's personal likes and dislikes. We welcome feedback from our readers and also that of manufacturers.