I agree to the constant voltage in asmuch as it leads to a constant acoustic power which lead to a constant SPL. Electrical power will not be constant because of impedance variations of the speaker(s), however constant acoustic power is what we want inorder to get constant SPL. Of course, the desireablilty of high frequency beaming in order to reduce reflections to improve imaging and such will even modify the desirability of constant acoustic power.

Paul

Not all multichannel music is mixed this way although I wish it was. I think they use 6 full range speakers because I have at least four DVD-As that have high frequency stuff in the sub channel (Toy Matinee, America: Homecoming, Fleetwood Mac: Rumors, Eagles: Hotel California). They also mix stuff below 40 hz to the "5" speakers, especially when they place the bass drum in any of them. I believe the bass of a bass drum is below even 30 hz.

SH: Not yet. That is my next project, as soon as I get tired of doing all the manual measurements...

The mystery is revealed: the key to the timings of the changes in the "Listening Challenge" can be found at:

http://home.earthlink.net/~soundhound/timings.html

Did anybody hear all the changes? Be honest!!

[This message has been edited by soundhound (edited October 15, 2002).]

I was able to figure out that the changes were at 30 second intervals based on the beginning of the track. The 1:00 to 1:30 segment has a very audible increase in - now, no one get upset or worried - analog hiss. It is barely detectible from 0:30 to 0:31. So, I just guessed, rather than heard, that the changes were of the same duration. Once the tune starts moving, I found it difficult to hear any change. I was particularly listening to the ride cymbal and the two saxophones and thought I could hear subtle changes, but nothing definitive at all. As for Miles, well, I think you can record him at 4 bits or 2 bits and his tone will sound pure . I could hear no difference through the trumpet passage.

I was going to do some more listening tonight but I couldn't resist following the link. I don't profess to be an audiophile but I really appreciated this exercise. I'm going to tell my wife that I should have heard the difference as clearly as day and night and, since I couldn't, that I need to upgrade again. She'll tell me that it's a lost cause and try to talk me into the Lifestyle system from that company in Framingham, Mass.

Thanks Soundhound. BTW, how did your first subject do?

DollarBill:

Glad you had fun with it. I have to admit that 12 bit and even 8 bit doesn't sound as bad as would be imagined. The dead giveaway of course is the increased hiss of the 8 bit. That's the dither noise. BTW Gonk has a copy of the entire CD that I made with entire tracks quanitzed at the three bit levels and a big selection of originally 24 bit reverb tails, fades, etc at the three bit depths. It was intended to show how digital audio can sound when delibrately or accidently screwed up. I'm sure he could forward it to you.

Well, my friend was totally snowballed. But I have to admit I didn't tell him before hand that the track was doctored. I just played it all the way through for him, and then asked him if he found _anything_ amiss. He didn't. Then I told him he had been listening to 8 bit audio, and he didn't believe me, and still swore that he could instantly tell the difference between 24 bit and 16 bit stereo recordings of the same program. At the time I didn't have any 24 bit sources like I do now, so I just had to shrug my shoulders and suggest we go out for dinner, and of course a pitcher of Margaritas.

PS: Nah, the "I couldn't hear any changes" argument didn't work on my wife, but enough of the above mentioned Margaritas, and maybe some flowers.....well.....

[This message has been edited by soundhound (edited October 15, 2002).]

I'd agree with what Paul says. To keep myself honest I wrote down my impressions before going to the 'cheat sheet', and I wonder if maybe the original isn't as clean as it absolutely could be. Some places I could (still can) hear what sounds like old fashioned distortion, maybe the original master was oversaturated or something (or maybe my ears need looked at).

Anyway, the 8 bit sections have got notations in them like 'distorted','sounds like a kazoo','Bad again', etc.

Several places in the 16 bit sections I could hear someting not right, at least to me, but apparently that was either the way it's supposed to sound (I'm more a strings guy) or the original is not all it could be.

I was not able to clearly hear transitions, except for a few where we switched from 8->16 or 16->8, but there are notations in the middle if some sections where we went from 12->8 or 8->12 where I noted things.

I suspect an ABX of this and the original would be more productive, but it is a great demo, one that will stay in my collection.

Nice work! I'm sending it on to Matt Hill.

The original recording was done in 1959. The instrumentalists are Miles Davis on trumpet, Bill Evans on piano, Paul Chambers on Bass, John Coltrane and Cannonball Adderly on sax and Jimmy Cobb on drums. I'm not familiar with the details of the recording other than it being a live take.

I wonder if a cleaner recording might not be a bit more revealing, but the point is, I think, still valid.

The recording does indeed have some saturation of the original tape. However it is not taken from an LP. The original was recorded on 3 track, 1/2 inch tape at 15 i.p.s. The remaster and remix for the original Columbia CD was done using one of the original tape machines to play the master tape. It was remastered in 20 bit with Sony's super bit mapping, which is the same thing as 'noise shaped dither' like I used on my doctored file.

I sent Gonk the entire CD that I prepared that has some modern and clean all digital recordings which play in their entireity in 16, then 12 and 8 bit. The effect of the bit depth reduction is easier to hear on the more current digital pieces. This CD will be making the rounds through this forum if anybody is interested.

One point in all this is that as the digital words get longer, it gets more difficult to hear the effects of the bit reduction i.e. it is harder to tell between 16 and 12 bit than from 12 bit to 8 bit. It is almost impossible to tell when switching from 24 bit to 20 bit, or to 16 bit. I have a number of original 24 recordings on hard disc and can do the switching on the fly to either 20 or 16 bit, from 24.

[This message has been edited by soundhound (edited October 16, 2002).]