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What does pre-delay do?

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What does pre-delay do?

PostPosted: Tue Nov 03, 2020 5:00 pm
by Demious
Yes of course, pre-delay is the difference in time between the original sound and the first reflection reaching our ears, thats obvious, but what is the effect it produces?
I heard someone say: when the source is close to the back wall, it takes little time before the sound reflects and travels along with the original sound, so the difference in time between the original and reflection is minimal (short pre-delay), while a source further from the back wall (so closer to the listener) takes more time to travel to the back wall and back to the listener's ear, resulting in a longer time between hearing the original sound and the first reflections. So, in short, short pre-delay positions the source further away and longer pre-delay positions the source closer by.
However, I heard someone else say: A longer pre-delay moves the sound source further away from the listening position. Which would be the opposite from the first statement.
So I though, the simplest way to figure this out, is to listen for myself and oh boy... I dont hear any difference in the position of the sound source at all! The only thing I hear is a difference in distance between a fixed sound source and the walls that are closer by, or further away from the position of the sound source.

So what is the actual effect of pre-delay on our perception of the positioning of the sound source?

I heard a 3rd person say: With digital reverb we have control over early and late reflections, so pre-delay isnt relevant anymore.
How does this fit in the story?

Re: What does pre-delay do?

PostPosted: Tue Nov 03, 2020 5:16 pm
by Kwackman
Pretty nicely covered in this article.
https://www.soundonsound.com/techniques ... e-knobs-do

Re: What does pre-delay do?

PostPosted: Tue Nov 03, 2020 5:25 pm
by Demious
Kwackman wrote:Pretty nicely covered in this article.
https://www.soundonsound.com/techniques ... e-knobs-do" target="phpbbpopup

Thanks!

Re: What does pre-delay do?

PostPosted: Tue Nov 03, 2020 5:33 pm
by Hugh Robjohns
Yep, the relevant paragraph from that technique feature is this:

Sam Inglis wrote:One way to understand the psychoacoustic effect of pre-delay is to imagine standing in the middle of a hall. A long pre-delay makes it feel as though the sound source is next to you in the middle of the hall. With no pre-delay, by contrast, it feels as though the source is far away on the edge of the hall, with the direct sound being immediately followed by the reflected sound.

So pre-delay is essentially the parameter that controls the perceived source image depth. longer pre-delays tend to make the source sound closer, while shorter pre-delays move it further back into the acoustic space.

Re: What does pre-delay do?

PostPosted: Wed Nov 04, 2020 2:38 pm
by rggillespie
This sounds like the answer to my prayers, if I've understood it correctly. So, for example if you had a vocal (the source) in a guitar, bass and drums setting and you wanted it to seem to be further back into the space. You'd add a reverb with a short pre delay and this would move it back in the space? Conversely a longer one to bring it forward. I'm always vaguely feeling that the various parts of a song aren't knitted together and some parts seem in front or behind each other in the imaginary recorded space. Whilst you can pan left and right I wasn't sure how to get things moving backwards and forwards in the stereo space. Pre-delay would a way of doing this?

Re: What does pre-delay do?

PostPosted: Wed Nov 04, 2020 3:07 pm
by Moroccomoose
That is my understanding. I think of it as how separated the reverb and source are. Obviously the more disconnected from reverb due to long pre delay, the more up front the sound.

I use a trick learned on this forum to have three delay fx feeding into the same reverb. One delay for near, middle and far. Then the reverb itself has no pre delay.

I also take a dry feed from each delay fx, eq'd according with increasing hf roll off, the further back it sits. I even did a spread sheet to calculate the delay times and the frequency roll offs for given room sizes and distance of source to listener! Happy to share if any one interested!

Re: What does pre-delay do?

PostPosted: Wed Nov 04, 2020 3:42 pm
by blinddrew
Interested! :thumbup:
I do the same thing but currently by hunch, which doesn't always work, so some starting numbers could be useful.
Thanks

Re: What does pre-delay do?

PostPosted: Wed Nov 04, 2020 4:30 pm
by Moroccomoose
Try this,let me know if it works...

https://1drv.ms/x/s!ApHK3Zf8zN6EkIw5_9M_XMRRJan0-w?e=Qc3iMY

This model considers both the onset of reverb delay and the time taken for the sound to arrive at the listener based on how far away they are.

If you don't want to bother with the direct delays, just subtract it from the onset of reverb delay to get the pre delay. They kind of null each other out a bit.

Stu.

Re: What does pre-delay do?

PostPosted: Wed Nov 04, 2020 6:02 pm
by blinddrew
It does indeed, downloaded now. Thanks for that. :)

Re: What does pre-delay do?

PostPosted: Wed Nov 04, 2020 6:06 pm
by The Elf
To push a sound away from the front of the mix it is not only about pre-delay - though that is an important ingredient. You also need to consider stereo width (narower when further away) and EQ (top and bottom less prominent).

Re: What does pre-delay do?

PostPosted: Thu Nov 05, 2020 8:29 am
by rggillespie
Thanks for the table and tips, I'll look forward to looking into it all over the weekend. That article's title 'reverb: what do all those knobs do' is a dream come true. I find I tend to use plugin presets without really understanding what all the knobs do on the plugin. It's good to have a primer to keep handy as a reference.

Re: What does pre-delay do?

PostPosted: Fri Nov 06, 2020 12:23 pm
by CS70
As the Elf says, depth in a mix can be manipulate by many things.

At the most basic, our perception of closeness is due to two things: the fact that high frequencies have lower energy and so dissipate within a short distance; and how the delayed reflections interact (filter) the original sound. The actual left-right position depends on the timing difference between left and right ear and again the reflections (because they'll be delayed anyways).

So any factor that affects either the high frequency content or the filtering with itself, affects the perception of the source position to the listener. Basically almost any mixing move does that a little bit (as almost any effect or gain change affects then HF spectrum of the source in some way) but we can limit ourselves to the stuff that potentially changes the HF a lot.

Still, this allows for uncountable different ways to make something sound in a certain way (i.e. change a vocal timbre, for example) but still moving it back and forth as it comes.

So if you EQ the voice so that it has a lot of highs (i.e. "it's very near"), you can use reflections to push it back again - and you can do that by using delays, reverbs, stereo effects or a combination of the two.

Do you want your deeeep bass feel very near and present? Easy, add an exciter if needed and EQ up some of the higher harmonics - suddenly your bassman is there being grabbed by the adoring fans.

Want to make something further back? Change the wetness of the reverb or delay - it will filter the original signal more and add/subtract HF. However, in this case often that filtering will add/subtract unevenly - something similar to comb filtering - which is why doing it that way is tricky (hence the good advice of keeping the reverbs tamed and it's not a "recommendable" way.. but it may work).

And so forth. All said and done, the relative depth of two sources can always be tweaked by looking at their HF contents . So a general workflow I use is to work out the timbres if needed, "place" the sources with "rough" HF filters such as reverb and delays (and their controls, including pre delay and dry/wet knob or send level) and then fine-tune the results with HF shelfs. But really any combination of moves that affect the relative HF content of the sources will do.