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Is there a simple way to build a configurable TOSLINK delay? Answered

Some TVs require 3 frames for the interpolation of tweening frames (and then there is also processing overhead time). With frames coming in at 1/24th for film or 1/30 for tv then 2 or 3 frames out of sync can look horrible and add several hundred millisecond delays. The TV's SPDIF is already delayed and works great, but downscales DTS to stereo (I hate you Blu-Ray!). So I need a delay on optical that bypasses the TV to get DTS to work.
I've done some research and found that the following products do a audio delay to help with sync problems with LCD TV (esp 120Hz) and TOSLINK on older receivers that can't add the required lip-sync delay.

The consumer level delays are made by:
Felston - $250
J.S. Technology (UK company) - £79 
Alchemy2 - $400-$450
Primare -£200

Bottom line, what does this take to develop: A TOSLINK receiver and transmitter. A MPU that can receive the serial stream store it in internal memory and read at a configured offset to transmit. Has anyone take up a project like this and be willing to post the intructions here. I hate to buy a new receiver just because of this, that would be wasteful.


If you can buy it for 79 quid, I'd buy it, you aren't going to get any change designing one. Its a job for an FPGA and a big circular buffer.


The J.S Tech box is only sold in the UK and it has no remote

Lets take the highest level of core DTS : 1.5 Mb/s = 192 Kilobytes/s (rare, usually lower rate than that). 100 KB should be more than sufficient for just about any implementation. I'm not sure why you suggest a FPGA, can you elaborate?. I thought a simple all-in-one would make sense. I guess 100KB cut down the list for MPUs, but maybe external RAM could be used

The point of instructables site is not to buy, but to build. It does not matter if it cost somewhat more (when it gets TOO expensive then I of course will balk).

Question remains: Have you done this and would you care yo share your designs and instructions with us?

An FPGA would be the cheapest way of doing it really. Its a simple, but fast buffer, and there are VHDL libraries for what you need to do.


Wow they are cheap AND they have much more RAM than most MPUs. I can get one with 18 Kb RAM and 60K gates for ~$6.. Now I need to figure out how to develop this. Look I'm pretty green with this stuff, I did a couple of computer electronics courses at University where we programmed NAND arrays and later the Intel P8051, but I can barely remember any of it. Any recommendations on guides to get started with FPGA and the VHDL libraries ? and how do I determine the number of gates I need ?

Fast too.

Easy to attach a stick of RAM too as well. 18 K isn't deep enough for your buffer, I don't think.

Next step is getting hold of a VHDL design tool. There are some you can get for free.


That is a fantastic question. I've wanted similar for quite a while - does the TV offer hdmi thru, or the audio amp have hdmi processing? It's the same dts signal but it might not get downscaled on the thru channel.

My receiver only has TOSLINK, SPDIF and 6 channel discrete. It only has delay for rear speakers (Max order of 5-15 ms). The TV passes on the correctly delayed digital audio through SPDIF, but cannot pass on DTS, it gives me stereo. Dolby Digital works fine.

Yeah, you're looking at a new receiver with that capability, or turn your tv's interpolation down a notch (makes me queasy anyway)...best of luck!

Hi frollard

I'd hate to have to buy a new receiver, but at the price they charge for these delay boxes its not really worth it to buy one unless you have really expensive audio equipment.

Even at the lowest setting on my TV there is still substantial image post-processing. This is common on LCDs since they add Dynamic Contrast, Pixel fill in, decoming, 2:3 framerate pull down and other processing. Worst is at 120Hz or 240Hz mode TVs where there is no escape from the framerate and subsequent frames required for fill in. I liked 120Hz initally, but now I turned it off since it makes film look like video.


it is a peculiar vision of the future where your tv pretends to know what the future holds...2-3 frames at a time :D

That said; TVs are getting very affordable these days, perhaps time to trade up the tv for one that has better lag characteristics.

Yes unfortunately all 120Hz and 240Hz tvs have this curse, no precognition here. The TV needs to SEE the three frames before outputting the first frame and then the tweening frames. Even though I might get less lag with 120hz off I still like it on for at least "some" content, plus even slight video lag annoys me. The only way around this is to have a receiver that supports HDMI 1.3 (contains lip-sync info passed down to the receiver) or to buy an audio delay with configurable delay time.

I would like to build a digital optical audio delay, not buy a delay or buy a receiver. Instructables.com is about building not buying readymade solutions.

right, and as steve says, you need, for even a few miliseconds, a LOT of cpu and memory to make it happen, it's not exactly a diy track without an electronics engineering degree. I can't even fathom the project.