Precaution for AC3 file generation

Sijon wrote on 5/27/2003, 10:28 PM
I recently traveled to Jackson, MS to make a 5.1 recording of a large Ruffati pipe organ. I directed low frequencies to the LFE (.1) channel. This is quite a sound and could be used as a leasebreaker should you need one! Vegas is a marvelous tool!

I decided to used DVD Architect and make a Music Compilation DVD using AC3 5.1 to send to the organist. After "burning" the DVD I checked it using several DVD players. I have an APEX AD-1200 that played the files instantly. But.....

I discovered that other DVD players evidently look at the bitstream and go through a series of algorithms before deciding to decode. A high-end Onkyo and a low-end Zenith both chopped off the first couple of measures on each track. I've not read anything about this in the literature but I went back and added two seconds of "preview" silence to the beginning of each AC3 file. This gives the player time to decide what's coming so that the beginning measures of each track are not chopped off. I may have to increase that time but two seconds satisfied those two players.

Comments

Bill_Wood wrote on 5/28/2003, 10:12 AM
Harold

What you are experiencing is the variable lock-up time of the different DVD players and receiver DD decoders. Unfortunately a DVD-A Music Compilation causes the decoders to drop out between tracks/chapters. Then it has to relock for the next track/chapter. Your adding two seconds of silence before each track/chapter gives the decoders time to come on line before the music starts.

BTW I also work with pipe organ recordings. Mostly transferring old, one-of-a-kind quad reel-to-reel tapes to Dolby Digital 5.1. To keep the 5.1 stream running all the time I use the "single Movie" DVD mode and put chapter marks in Vegas 4 and render both an MPEG-2 video olny mpg file and the Dolby Dig 5.1 ac3 file. That way the chapter points work in the final DVD. I often add simple titles in to video track to identify what selection is playing.

Bill
Sijon wrote on 5/28/2003, 11:50 AM
Bill

Thanks for the explanation. Obviously there is a lot more to DVD than CD and a misstep with a commerical release can be costly! I forgot to add in the former post that, apparently, digital silence is not added between tracks as with CD Disc-At-Once (at least as far as I can tell), o using the new Master effects channel volume envelope in Vegas 4, do a quick fade to silence and then extend the length of the file so that I have a total of 8 seconds of silence. I know 7 seconds is "the standard" but I've found over the years that the ear/mind has persistence and will hold the sound a little longer than 7 seconds. So if the succeeding piece is in an unrelated key the clash is startling. The alternative is to use a succeeding piece in a harmonically related key but that's not usually possible in situations like live symphony recordings.

I just looked in the archives for you for an organ tape copy I was involved in back in the early 1970's. At the time I was Technical Director for The United States Army Band (Pershing's Own) in Washington DC. On weekends I did service work for Audio Associates, a high end shop owned by Mike Zazanis, "the Great Golden Greek." (so called because everything he touched turned to gold) Glenn Glancy, who owned United Sound Recorders, contracted with Marilyn Mason, a concert artist of the time, to come to Washington and perform on the organ of The Shrine of the Immaculate Conception, the 7th largest cathedral in the world. The recording was made in two channels and then Marilyn returned to New York (she was high dollar). We got from Mike Zazanis two of Rudy Bozak's high-end speaker systems called Concert Grands. This was an infinite baffle measuring about 5' x 5'. We placed two of those up on the wind chests of the organ and played the original two channel recording while experimenting with rear-of the-room microphone placement and re-recording the sound using the original room ambience. The resulting Ampex AG-440-4 recording was unbelievably good! Unfortunately the SQ encoded LP was not as stunning. And, of course, LP's always evidenced tracing distortion that used to drive me up a wall!

Anyway, my search turned up the LP but not a copy of the tape. Many of the tapes from that time used a binder (used to adhere particles to the backing) that proved defective over time. It deteriorated to "goo." When you try to play it back goo begins to build up on the recorder heads and finally the tape just stops. About all you can do is throw it in the trash. So that may be what happened to my copy.