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I make presentation software, and we have the ability to export that presentation to a video. Lately, we're trying to add the ability to choose a soundtrack to attach to that exported video. We want the soundtrack to fade in/out.

I'm pretty unfamiliar with the theory behind fade in/out and have some questions so I can understand it.

  • What length is optimal? (If you had to choose a single length, what would you choose so it doesn't seem like it's ending the video too early but isn't abrupt either)
  • What kind of function do you use to reduce the volume? Is there some common formula or technique to calculate the volume level at a point in the fade?
  • How do you deal with situations with really short audio files? For example, a 2 second fade-in and fade-out wouldn't work on a 3 or 4 second audio file? Is there some % we can use or do you just disable it completely?

Thanks in advance for your expertise!

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Sorry, but I don't have the ability to ask clarification on your question. Do you mean you're adding the ability for the end-user to choose a soundtrack themselves or you're asking about you adding he soundtrack before exporting the video?

Assuming the latter...

For me I try to first see if the song's natural ending can work before trying a fade. This almost always sounds better to my ears.

I hate to hear a fade out when it sounds like the music is increasing in intensity. Even though it's just a background song, I personally like a beginning, middle, and end.

Most songs will have some transition points that are perfect cutting areas to piece in a later part of the song. I do this a lot with 30 sec commercials when I only have longer pieces of music. Essentially building a 30 sec cut out of a 2.5 min song.

The downside though, it takes more time and experience, which you may not have. But upside, they will sound far more natural. (If done correctly).

However, if you need to simply fade out, I agree with coaxmw in that you just have to feel what's right for the specific piece. Just imagine you are the end user and what his experience is at that moment. That should help you decide.

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  • We're giving the end user the ability to add a soundtrack. We don't have the ability to give users complete control over fading, so we were looking for some generally accepted best practices (such as, how do you decide what the volume will be at point X in the fade - is there some good functions/formulas)? – Joe Marks Jan 30 '14 at 5:34
  • Ah, I understand. You're limited with your options in this case. I would have to go with a standard linear fade in this case. For most lengths you can experiment to see what sounds good to you. But for really short ones you can probably fade somewhat quicker. Again, whatever sounds good for that length. – OutRecording Jan 31 '14 at 7:09
  • One suggestion I can give would be to purchase tracks that have several cuts (3 min, 1'30, 1 min, 30 sec, 15 sec, for example). Or create them yourself if you have time. Them when the user chooses a song for a specific presentation, the software can find the cut with the length closest to the presentation length. It won't be perfect, but will allow the song to develop some and possibly fade out towards the end. Hope you're following my meaning. I'm not sure if I'm coming across correctly. – OutRecording Jan 31 '14 at 7:13
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It really needs to be based on what your fading out, how loud it is at the start of the fade, if anything else visually is happening, tempo or pace of the music, instrumentation. It's all what feels best to you. There really is no right or wrong way. Today alone I've mixed one spot with a 4 second music fade and another with a 5 frame fade. Most are probably 1-2 seconds.

| improve this answer | |
  • We're giving the end user the ability to add a soundtrack. We don't have the ability to give users complete control over fading, so we were looking for some generally accepted best practices (such as, how do you decide what the volume will be at point X in the fade - is there some good functions/formulas)? – Joe Marks Jan 30 '14 at 5:34
  • I'd say the most common type is a pretty linear fade where the volume is one half, halfway through the fade. Their are also logarithmic fades that sound better on some material but the linear one is probably the most basic/foolproof and works most of the time. – coaxmw Jan 30 '14 at 6:12
  • Ok, thanks a lot for your help! How do you suggest we deal with short files (i.e., less than 5 seconds or so)? Is there some percentage fading we can apply (fade the last 10% of the file), or is ignoring fading altogether a better option? – Joe Marks Jan 30 '14 at 22:35
  • It's hard to say without hearing the audio but maybe a half second fade just to get the user into and out of the content a little smoother. A fade out is used more commonly than a fade in for music because usually you would start the file on beat. – coaxmw Jan 30 '14 at 22:39
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There isn't really a right or wrong answer here. Fade lengths can very significantly. Algorithms tend to either be mildly logarithmic (fade quickly at first but then slow down for the last bit) or linear. They can also be more curved where they start exponentially with a slowly increasing rate of reduction and then half way through switch to a logarithmic approach to make it fade out smoothly. This is perhaps the most smooth as it doesn't rapidly change the volume, but it is also harder to implement. Linear normally is sufficient though.

You will probably want to provide the user with the option to choose a length. You probably don't want to go shorter than a second generally, but you can also make a big impact on the length it takes based on how you fade out. You also normally don't gain a lot beyond 3 or 4 seconds since you are often fading out content at that point.

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