Why do certain sounds have a very loud pop when you stop/pause or start the sound.

andrewoot
andrewoot Website User Posts: 1 Just Starting Out

if any professional here knows about music and sounds engineering, can you explain why sounds have this sort of pop noise only when you pause at the continuous sound, does it have something to do with the program that i'm recording the sounds or the the sound waves and frequencies that makes for such effect. You can hear the sound hear https://www.youtube.com/watch?v=UPtHagd5stc

Answers

  • Triem23
    Triem23 Moderator Moderator, Website User, Ambassador, Imerge Beta Tester, HitFilm Beta Tester Posts: 19,956 Ambassador

    Sure!

    Audio has two basic components - frequency/pitch and volume/amplitude. Audio is just a vibration in a medium - air, water, even solids. When air vibrations hit your eardrum, it causes your eardrum to vibrate. This generates electric impulses in the auditory nerve. Your brain then translates this electric impulse as "sound."

    A microphone is like an ear. A membrane in the mic vibrates when hit by the moving air. The vibrations move a magnet attached to the membrane, which generates electric impulses. In analog audio the electric impulse passes to the next gear in the chain, in digital audio the electric wave it converted into binary code.

    A speaker does the same thing in reverse. An audio signal varies an electric impulse which causes a magnet to vibrate. This magnet is attached to a membrane which vibrates which pushes air. That vibrating air then hits the eardrum.

    Incidentally, the old philosophical question of "if a tree falls and no one is there to hear it, does it make a sound?" has a boring answer. Yes. The falling tree still vibrates and moves the air. Even if nothing is around to hear it the air vibrations exist.

    Ok, that's the super-simplified basics.

    Let's take a look at this diagram.

    This is a simple sine wave. If an audio wave, this would represent a pure tone.

    The vertical axis represents amplitude (volume/loudness) of the sound while the horizontal axis is time. For audio if we had more waves in the same amount of space we'd have a higher pitch, fewer waves in the same space, a lower pitch.

    For your question, we only need to look at the vertical. The horizontal line labeled "time" is the "zero-point" or "zero-crossing." This represents the instant in the wave where amplitude is zero.

    Slicing a sound or starting/ending a sound on the zero point is the goal. There will be a smooth transition. Slicing anywhere off the zero point can cause a "click" or "snap." Especially if you cut to a new sound, and most especially if you cut from (say) part of the wave above the zero line to something below the zero line (or from Below to above).

    Let's look at this image.

    The top part of the image shows a cut between two waves, not on the zero point.

    Using a speaker as the example, anything "above zero" represents the speaker cone pushing forward from rest. "Below zero" is the speaker pulling back from rest. That cut from the wave above zero to the wave below zero means the speaker snaps back in less that 1/44000 of a second, and THAT'S your click.

    As you can see, the rest of the image shows how, by changing the trim points to zero crossing, you get a nice smooth wave. No click.

    Some NLEs (like Vegas Pro) automatically apply a short fade to any audio edit (about 5 milliseconds) to prevent clicks. Dedicated audio editors have a "snap to zero" feature that automatically moves a cut point to the nearest zero crossing to prevent clicks.

    Hitfilm doesn't do either. Hitfilm cuts audio on the frame boundary of the video frames. (1/24th of a second to 1/60th of a second, depending on project frame rate), while a digital audio editor allows cuts down to the "sample rate" (1/44000 of a second, 1/48000 of a second, or even 1/96000 of a second!). Obviously sample rate edits make it easy to find a zero point while, a Hitfilm audio edit might not be able to hit a zero point.

    In Hitfilm, if an audio edit is causing a click you have two choices - add a one frame fade out to remove the click or... Don't edit your audio in Hitfilm and use a dedicated audio editor.

    Now, if I play back the video you linked and drag the time cursor around, almost every time there's a click as I skip to the new time. Why? I didn't happen to skip from a zero point to a zero point, so there's a click.

    Hope this makes sense! 😁