Surround sound delay line

[ialpha]

i'm trying to design a simple line level surround sound decoder and would like some kind of delay line for my rears. I remember some years ago seeing a circuit that used a Mitsubishi M65830 delay line, but these haven't been available for some time. Anyone know a similar IC that would be suitable. also any other ideas of how I could achieve this would be fantastic.

thanks

[ialpha]

sorry i posted this twice by mistake. left my browser open and clicked back. not sure if thee is anyway to delete it

[Ken Newton]

Please define what you mean by, "simple". For instance, are you looking to decode primarily DolbyDigital, DTS, and their variants? Is this for a movie surround application, for a music surround, or both equally? What is your desired speaker configuration - main channels, surround channels, and constraints on their locations within the room? I ask these questions because the answers can greatly affect the line-level processing solution/implementation needed.

[ialpha]

The system is for both music and movie home surround. I perhaps shouldn't use the term "decoder" its bit misleading. I found this project by Rod Elliott and it outlines perfectly what i want to do. the delay ic he uses is no longer available. basically I'm trying to create a line level Hafler matrix with a delay on the rear channel. The front speakers are bi-amped 60W, haven't built the rear amps yet but was thinking around 40w or so. its a mid size lounge approx 6Meters x 4M. No Dolby decoding etc I possibly should of put this in analog line level forum but I figured this will end up been a digital delay.

[Ken Newton]

Okay, I suspected that you might be attempting something like the Hafler matrix. Following, is my advice based on having utilized a Hafler matrix surround setup for about 20 years. I've find that that a delay processor is not needed. I suspect that because the Hafler matrix extracts a correlated natural ambient field from a recording, the relative delay of the "surround" information is inherent and you don't need to synthesize a delay. The natural ambient field (if any) during a recording session arrives naturally delayed from the direct sound on the recording.

I use two floorstanding speakers, stereo left and right, and use two mini-monitors placed on stands behind each floorstander. I get the most realistic soundfield when each mini-monitors is narrowly angled from behind it's respective main speaker to radiate down along the nearest sidewall adjacent to your listening position. I've tried many other positions for the "surrounds" but that seems to work best, IMHO. You could simply connect the surround speakers as Elliott shows, although I find it sounds better if the two surround speakers are wired out of phase with each other. Also, I find that the level needs to be set way down, around -12bB, relative to the main channels. The direct speaker version of the Hafler matrix will already inherently be down 6dB if the sensitivity of the surrounds is the same as for the mains.

At the line-level, you would need to implement a difference amplifier circuit. I should think that the resulting surround channel information would be of higher quality without having undergone the indignities of an analog delay-line.

[ialpha]

Thank you for this very helpful advice, I have just started the design stage of my new amp, once I have that built and tested ill get into building a simple Halfer matrix. sometimes simplicity is best.

[Ken Newton]

The effect of the Hafler matrix never ceases to bring a smile to me face when listening. Just remember that, at least for music, you want to have the the surrounds down in level. If they are too loud it spoils the effect. Just a little goes a long way toward revealing the natural three-dimensionality and presence locked within existing stereo music content.