Processing delay issue with radio microphone

[JSalisbury]

I was at an event with a modern radio microphone used to walk round the conference audience. The pa speakers were quite loud. When I tried to speak into the microphone there was a very short delay. This delay made me very difficult to speak. I was about 8 meters from the pa speakers. It was a sennheiser radio mic with LCD display. It was a allan and heath analog desk. What are the causes of the delay?

[J Pearce]

The acoustic delay at 8m is around 23ms. That's enough delay that it could upset you.

The analogue sound desk will introduce absolutely zero delay. Some sennheiser radio mics with LCDs are digital, some are analogue. The digital mic/receiver combo introduces around 3ms of delay/latency. The analogy setup should be entirely latency free.
There may have been a system processor or digital amplifier introducing somewhere between 0.7ms and 5ms of additional delay.

I suspect the main component of your issue was that you were 8m away from the speakers. This is a significant contributor to the use of IEMs on large scale events - it's very hard to keep arrival times constant.

With practice one can get used to speaking against a delay, the FOH paging system at a previous job introduced 20ms of processing delay and another at least 30ms of acoustic delay between speakers and the location of the paging mic. At first this really tripped me up, but it didn't take long for me to focus on my voice both acoustically and via bone conduction rather than the paging system.

[Jivemaster]

POSSIBLY partially  a deliberate delay to reduce the chances of feedback when a mic is pointed at a speaker.

[Dave m]

Yeah, my first thought was a deliberate delay to stop feedback.

I used to wind up mates in a band by using the delay in sound checks so that they only heard the delay and no original. One guy in particular couldn’t speak at all once you hit the right setting.

I think there was a study on stuttering that suggested a connection between the brain processing audio info and a stutter? Maybe the person hears “late” compared to people who don’t stutter?

[sandall]

1 hour ago, Jivemaster said:

POSSIBLY partially  a deliberate delay to reduce the chances of feedback when a mic is pointed at a speaker.

POSSIBLY, but doesn't everyone have a "feedback destroyer" in their rack to keep them awake (or left bypassed if they don't want to be kept awake)? I suspect Jon has the answer.

[samchurchill]

Were the PA speakers that you were 8m from at the front of the room, or a set further back to boost the sound for those sat further back?  Ones further back are usually called “delays” because they should be intentionally delayed from the front set of speakers so that they’re time aligned.

Even if they were the front set of speakers, sometimes even they are intentionally delayed to align with a loud acoustic instrument on stage e.g. drums.

(Perhaps an obvious one, but hadn’t been mentioned above yet.)

[sunray]

Sorry I have to disagree, 8M is far to short a distance to introduce enough delay to make speaking difficult.

If the mic level is 'quite loud' I imagine there is some form of feedback destroyer in circuit and I'm starting to find the levels of DSP  being introduced are the culpret.

A short while ago I put a basic system out on a job. Inter-m 300W pod, 2 speakers and 2 cheap radio mics for a meeting of around 100 people in a hall that holds about 150 with absorbant ceiling tiles, additionally the back of the hall (Actually one side as the group use the hall sideways) has cork noticeboards virtually the whole length of the wall. A nice hall for sound with no noticable reflections, even when completely empty. I've used  the same system for the job on a very regular basis (maybe 4-6 times a year for 10+ years) initially I'd stay and operate but one day I had an appointment elsewhere and left one of their members in charge. That has been the format ever since.

I set it up, checked all working and left it in the guys very capable hands. I try to get back to rip near the end of their meeting to make sure it sounds OK and sample the obligatory bread pudding.  It sounded aweful with a significant crazy, crazy very loud and late echo, far louder than the GBF was capable of. Their guy was very apologetic that the speaker complained it wasn't loud enough and plugged his DSP unit into the effects loop.

[J Pearce]

Cool story. Hope you enjoyed the bread pudding.

The precedence effect (sometimes called the Haas effect) would suggest that a 23ms delay should be below the human threshold of delay perception - but perception is variable, and I suspect many of us here could detect 23ms when system tuning - whether as a phasing or as an echo.

In another vein - 8m plus a reverberant room might have got there. A horrible reflection off a hard wall perhaps?

Or 8m is a rough estimate and actuallt it was much further?

Really, without knowing the system setup we’re all guessing.

Maybe there was a 50ms delay tuned in somehow - not something I’d do or have seen done, but there’s a whole world out there.

I think the important point I wanted to make is that there is no way the ADC, processing, and DAC latency from a digital radio mic or digital sound desk would have produced the effect described by the OP.

Edited August 13, 2022 by J Pearce
Clarity

[sunray]

On 8/13/2022 at 9:32 PM, J Pearce said:

Cool story. Hope you enjoyed the bread pudding.

The precedence effect (sometimes called the Haas effect) would suggest that a 23ms delay should be below the human threshold of delay perception - but perception is variable, and I suspect many of us here could detect 23ms when system tuning - whether as a phasing or as an echo.

In another vein - 8m plus a reverberant room might have got there. A horrible reflection off a hard wall perhaps?

Or 8m is a rough estimate and actuallt it was much further?

Really, without knowing the system setup we’re all guessing.

Maybe there was a 50ms delay tuned in somehow - not something I’d do or have seen done, but there’s a whole world out there.

I think the important point I wanted to make is that there is no way the ADC, processing, and DAC latency from a digital radio mic or digital sound desk would have produced the effect described by the OP.

Oh yes her bread pudding is the best... oops second best, sorry Mum.

23mS is certainly detectable, (I've only ever set up delay by ear) but I think anyone would be hard pushed to be distracted by it while speaking, music/singing is a different matter. The reflection is of course a different story and I once had a problem with an air duct with multiple grills into a very large boardroom. Eventually is was sorted by the ventilation company.

I find I notice the latency with digital radio mics but no I agree it's not going to be the cause, however working from your comments it's fewmS plus a digital desk plus the DSP in the amps and suddenly 23ms becoms 33mS and a reflection from the back of a 15m hall give an echo at double that.

[david.elsbury]

It’s a bit rude to invalidate someone’s experience by saying the effect of “I don’t believe what you say you experienced “ ☺️

[sunray]

1 hour ago, david.elsbury said:

It’s a bit rude to invalidate someone’s experience by saying the effect of “I don’t believe what you say you experienced “ ☺️

Who is this aimed at?

If me I apologise if I've given that impression but I don't dispute OP's observations, I have heard far too many systems so badly set-up that have the same issue.

[david.elsbury]

4 hours ago, sunray said:

Who is this aimed at?

If me I apologise if I've given that impression but I don't dispute OP's observations, I have heard far too many systems so badly set-up that have the same issue.

You.

[JSalisbury]

Ok,

Some updates.

1. I am senstive to line echo, I do have a hidden stammer. I did have to get the London Fire Brigade to adjust the echo cancelation on their 999 lines as it nearly made it impossible for me to call them to a suspected house fire.

2. When I was sat middle of house on about row 3 I could use the microphone (the desk was in stereo and the microphones were panned to center), I suspect the channel gain was also set lower.

3. When I was having difficulties I was in about row 7 and towards house left, I would have then had about the 23ms from the left channel and the right channel was even further away. The speakers were quite loud and I was suppriesed it wasn't hooting.

4. I suspect that next I will be the one doing the sound desk. There were a number of desk microphones on the stage on a desk infront of the presnters but were a couple of feet from their mouths. As you can imagine there were a lot of sqeeks and howls, this caused me to mutter loudly from the audiance about the Barkhausen criterion for oscilation and explained to move the microphones closer and drop the desk gain.