Blind Shoot-out in San Diego -- 5 CD Players

Ctm_cra, You guys apparently spent a lot of time eliminating as much of the varibles involved in blind A/B testing, but I remain curious about a couple of things I have always felt might affect the outcome.

The first issue is stereo imaging. One of the hall marks of great 2 channel stereo systems is its ability to convey with absolute accuracy the information in the source recording. Nearfield listening, within the parameters of the system set up requirements and room possibilities, is the most revealing in this respect. (Other set ups for far field, more reverberant sounds, like omidirectional or bi polar speakers may sound 'wonderful' but are not necessarily accurate or reproducable in other environments.

My first question - How can five folks hear the same sound at the same time? Only one can sit in the sweet spot and we all know that listening off the sweet spot may be good but I doubt that anyone will consider it accurate. Or do you feel that stereo imaging capabilities of the digital devise, or the set up, is not relevant?

The next question has to do with short term perceptions that are based on high frequency information. That is, can you tell when the sound of the higher frequencies are more detailed due to 1) A slight mid-range recession, 2) A slight elevation of the high frequencies, 3)Shortening of the decay time of the signal (imparts a fast sound and a clarity due to the shopping off of the trailing edge of the signal, or 4) The excellence of the sound is simply the absence of any distortions what so ever.

IMHO a slight increase, or clarity, in high frequency information can have a very audible effect in stereo imaging, but the reason for the apparent increase is very important. If its for any reason other than increased clarity its likely to induce some fatigue factor in long term listening sessions.

The question - how can you resolve these issues in short A/B listening with any assurance that the sound that you find attractive under such conditions will survive long term listening under controlled conditions?

Am I missing something here? Are the assumptions leading to my questions off base?

When I do sighted A/B tests at home - which I very rarely do, because I find longer (usually measured in hours or days) experience with a component much more reliable - I always do A/B/A/B; or AA/BB/AA/BB; or A/B/B/A, etc. I do this because the second time I hear a piece of music I notice (or "hear") more than I did the first time. This can result in a bias for the second component. I realize that this mixing of the order was probably not possible to do, given the logistics involved in this very well-thought-out test. I'm just adding my thoughts here to the discussion; i.e., not arguing a point of any kind.

Jfz - Nice approach you have. We did a mixture of this actually.

During round 1 we learned a number of things. Important among these was the fact that the voters (although they could not see the players) could tell the one being used because they can see which one received the CD we wanted hear. So we decided to mix things up as detailed in my previous response to Tbg. Although we kept evaluating the choral track before the orchestral recording, we mixed up which player started each pairing and THIS WAS DONE FOR EACH TRACK. Thus, for any pairing being evaluated we did not necessarily begin with the same player for the NEXT CD used. After round 1, the voters did not know which player was playing at any given time.

I wanted to address your comment about hearing more the subsequent times you listen to a recording. I agree and some would also say that their focus changes during the second or third tries, when compared to the first time they hear a recording. There was really no way to address this equally for all voters. Three of the five voters know the Rutter piece very well as we have used it in previous evaluations. Only two of the voters know the Bernstein recording. We felt it was important for each voter to have many opportunities to hear each track so they can confidently cast their votes. Here is a little more detail on our listening process for EACH TRACK...

1) With the correct input selector and volume levels set, we loaded both players, one with the test CD, the other with a dummy CD. We then listened to a predetermined point on player A. For the Rutter piece this was at the 2:08 mark and at 2:44 for the Bernstein piece.
2) Rewind and listen again but for a shorter time. Up to 1:13 for Rutter and 1:38 for Bernstein.
3) We asked is any voter needed additional listening and, if so, we would repeat 2) above
4) Unload both players, switch CDs (the location of the one being tested is not revealed/visible to voters)
5) Reload both CDs and select the appropriate line input of the preamp and make the necessary volume adjustments as predetermined by the level matching done during the set up for both players.
6) Repeat 1, 2 and 3 above for player B.
7) We asked if any voters wanted to go back to player A, and we would repeat steps 4, 5, 1, 2, and 3 for everyone. This option was done only for one pairing – the DCS vs. the Meitner.
8) Immediately vote with show of hands (no discussions)
9) Repeat the process for the next recording.

One more thing to note, for subsequent pairings and even in between each pairing, we also switched the input selector to which the players were connected on the preamp. Even though we were assured by its manufacturer that Line 1 is identical to Line 2 in every way (materials/parts as well as specs), we wanted to vary this too, just in case ;-)

Newbee – You ask some important questions. All five voters sat in the same seats throughout all comparisons, so the perspective of each listener never changed.

Certainly none of the side positions is as revealing as the sweet spot, which can accommodate two people -- one in front of the other. However, we spent a considerable amount of time in advance of the event to position the other seats so that acceptably focused images and a convincing soundstage is perceived from the other three positions -- two on either side of the sweet spot in the back row and one to the side in the front row. None of the voters raised the concern about the lack of image focus or not being able to hear dimensional details. Later when discussions were allowed, the three voters sitting at the side positions were surprised they were able to tell each player’s ability to present a focused image and believable soundstage. These side perspectives may not be correct, but it was the best we could do given our time constraints.

I do not know if the other voters prefer nearfield listening. However, I know they can easily recognize good, focused imaging and excellent soundstaging when they hear it. However, stereo imaging and soundstaging capabilities, although important, are only two of the many criteria each voter had to keep in mind as when they listened. In fact we did not prediscuss or define these sonic parameters. We simply asked each voter to listen, compare and honestly and confidently cast a vote as to which player they liked in each pairing.

The speakers used are neither dipoles nor horns. The drivers are not horn loaded, do not use ribbon tweeters, and has excellent off axis response. It is appropriate at this point to provide the room dimensions (hopefully this info partially addresses other member’s curiosities):

width - 12 feet
length - 15 feet (see * more info)
front row - ~9.5 feet diagonal from front of each speaker
back row - ~11.5 feet diagonal from the front of each speaker

The wall behind the seats has a central window, which is covered with 2 layers of fairly thick curtains. The floor is wool carpeted with foam insulation underneath and this is supplemented by another 6x8 ft area rug on top. The cement foundation is underneath the carpet. Spikes are used at the rear of each speaker to couple them to the foundation. A single Finite Elemente Cerapuc is used in front of each speaker as a vibration control treatment.

*There is no wall behind the speakers and this contributes greatly to this system's superb imaging/soundstaging. The lack of wall behind the speakers also partially contributes to a flat FR response measurement from the sitting position. The room node interactions are negligible at +1.5 dB at 80Hz and flat at nearby frequencies. My very first post includes details of the very good in-room, from-the-listening-position SPL measurements. These data also clearly detail that there are no “slight mid-range recession” or a “slight elevation of the high frequencies”.

I do not know if there is “shortening of the decay time of the signal (imparts a fast sound and a clarity due to the shopping off of the trailing edge of the signal”. Please pardon my obvious lack of technical knowledge, but I can only guess this is more perceived than measured, yes? This system has never been described as fast, slow or muddy. Besides its superb imaging, soundstaging and layering/delineation capabilities, it is also dynamic and articulate, while also having a tonal balance that results in a believable representation of real instruments or voices. These along with the system’s overall musicality and resolving ability are the reasons why we keep using it for our comparisons.

I cannot confirm “the excellence of the sound is simply the absence of any distortions”. We never measured this system in this regard so we have no meaningful information to share. Suffice it to say that there is distortion (what system doesn’t), but none of its symptoms have ever noticeably/audibly surfaced. We’ve used other systems in the past so this is not the only one with which we have experience. However, during last four years we’ve done comparisons using this system, no one has ever commented something that would lead us to investigate if distortions are an issue.

As to the type of listening fatigue I think you described, not one of the voters mentioned or commented anything that had to do with system edginess or harshness. Another member already raised concern about careful AB comparisons for 6 hours. We took plenty of breaks in the kitchen and family room areas, while the set-up, level matching, and blinding was being done for each pairing. Fatigue of a different kind eventually set in. We would have kept going were it not for one voter having to leave, another voter needing to join his family and the others wanted to go out and get steak ;-)