Copper or active/optic HDMI for smallest audio delay over 15m?

kryten22uk

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This is not for a traditional TV setup.

I'm using a computer system which measures brain activity and issues audio signals for it to measure the brains reaction. In doing this, the system sends the audio data down an HDMI to the soundbar/speaker on the monitor. The HMDI is 12/15m long. Therefore I need a solution where I minimise any sound delay and quality as far as possible, such that the audio information sent from my system is received and processed by the speaker in the quickest time possible.

Now, I know that for such distances the recommendations for AV setups is to go active/optical for the HDMI. But I dont need to transmit high quality video signals, only audio (there is some basic video graphics which get sent down HDMI too, but not high datarate).

So I wondered whether I should be using a traditional copper wire HDMI cable or still go with an optic/active HMDI? I was thinking perhaps the additional processing that the active HDMI male heads do in the optic cables might delay audio more than a copper wire. But then I dont know how much a long copper HDMI also deteriorates audio quality.
 
I think you would have to try both options and decide if one or other works best in your setup.

Happy to help out if you are in the UK.

Joe
 
This is not for a traditional TV setup.

I'm using a computer system which measures brain activity and issues audio signals for it to measure the brains reaction. In doing this, the system sends the audio data down an HDMI to the soundbar/speaker on the monitor. The HMDI is 12/15m long. Therefore I need a solution where I minimise any sound delay and quality as far as possible, such that the audio information sent from my system is received and processed by the speaker in the quickest time possible.

Now, I know that for such distances the recommendations for AV setups is to go active/optical for the HDMI. But I dont need to transmit high quality video signals, only audio (there is some basic video graphics which get sent down HDMI too, but not high datarate).

So I wondered whether I should be using a traditional copper wire HDMI cable or still go with an optic/active HMDI? I was thinking perhaps the additional processing that the active HDMI male heads do in the optic cables might delay audio more than a copper wire. But then I dont know how much a long copper HDMI also deteriorates audio quality.

HDMI is a very bad choice of interface for such a system.
HDMI carries audio embedded within the Video signal , if there is no video signal , a dummy one is created to insert the audio signal into.

There are inevitable delays in separating , processing , and aligning video and audio at the sink end of the chain , but for AV thats OK because all that matters is that the video and audio are in Sync.

For measuring any kind of reactions in terms of brain activity and user interaction on hearing a sound , HDMI is going to be a disaster. ( Active or Passive)
You would have to be able to exactly work out the processing time of the interface and subtract that from the user interaction time , and with HDMI that is going to be so variable as to be almost impossible.

Resulting data would be useless due to the inaccuracies introduced by the totally unsuitable interface.
Peer review of any paper produced would be a bad bad day for you.
 
It does seem an odd/poor choice, it would be good to understand the complete signal and recording path and how the Soundbar is being utilised.

Joe
 
Oh, that's not great.
The system is in effect a laptop. It has a USB-A, USB-C 3and 3.5mm jack as outputs. The standard setup is to use earphones plugged into the jack, but I was looking into options where earbuds are not preferred or possible with the client. Hence need an external speaker solution. I thought maybe use the TV soundbar, hence hook it up via HDMI. But I could instead use traditional external speakers with a longish wire into the jack socket.
 
Which Laptop do you have?

As @andy1249 says are you logging data on the laptop and the speaker is simply an audible cue for you/the patient?

Joe
 
Which Laptop do you have?

As @andy1249 says are you logging data on the laptop and the speaker is simply an audible cue for you/the patient?

Joe
The laptop is a Microsoft surface pro i7. It's hooked up to other external hardware which reads/amplifies/transforms brain signals via sensors place in various positions on the head and ears. The programme plays music to the client. When certain subconscious brain activity is sensed (nothing to do with the music itself), the programme pauses the music for a fraction of a second. The brain then reacts in a certain way to the break in the music.

I guess that if there is too long an audio delay between the programme sending the 'pause' audio signal and the brain hearing the pause, then the brain activity to which you are trying to interrupt could have passed, making the process pointless.
 
The laptop is a Microsoft surface pro i7. It's hooked up to other external hardware which reads/amplifies/transforms brain signals via sensors place in various positions on the head and ears. The programme plays music to the client. When certain subconscious brain activity is sensed (nothing to do with the music itself), the programme pauses the music for a fraction of a second. The brain then reacts in a certain way to the break in the music.

I guess that if there is too long an audio delay between the programme sending the 'pause' audio signal and the brain hearing the pause, then the brain activity to which you are trying to interrupt could have passed, making the process pointless.

Simple speakers and copper wire setup then , with possibly the pc being used only as a remote on/off switch for the source of the music.

Stay well away from complicated interfaces like HDMI , too many variables in terms of processing and delays.
 
You could do something similar to REW with it's timing reference. If you have a mic that's connected to the same system as the sensors on the patient's head, then send a known test tone and have that measure the delay first (before every run). Whatever that delay is, is the delay that the system is adding in. Take that away from the recorded patient measurement and you'll be close. With REW it uses the same input for the timing tone as the measurement, so the chains are identical. This wouldn't be the case for you so it might not be as accurate as you need.

I wonder if that concept gives any ideas or could be applied in a way that's useful?
 
You could do something similar to REW with it's timing reference. If you have a mic that's connected to the same system as the sensors on the patient's head, then send a known test tone and have that measure the delay first (before every run). Whatever that delay is, is the delay that the system is adding in. Take that away from the recorded patient measurement and you'll be close. With REW it uses the same input for the timing tone as the measurement, so the chains are identical. This wouldn't be the case for you so it might not be as accurate as you need.

I wonder if that concept gives any ideas or could be applied in a way that's useful?
Thanks for the ideas, but this system doesn't quite work in the same way. We don't take recordings on the response to the noise pause, so there isn't any reference timing or similar to subtract and audio delay from.

I have now received a response from the manufacturers that the audio delay is not of particular importance. Its a bit puzzling but there is a lot about the system that is IP and they don't fully explain. We dont use the system for scientific research, its more a therapy machine.

I think all, in all, I'm still going to opt for satellite speakers either side of the chair, wired via the jack, as suggested above.
 

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