Editing audio to an exact length

  • Thread starter Thread starter douglasfur
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douglasfur

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Hey there,

I was curious if anyone knows of a program that can edit the length of an audio file extremely accurately. IE to a millionth of a second or better. I usually use garageband for this but it only goes to the thousandth of a second before it rounds up/down.

I am running a Mac. Cheap or free is my preference.

Thanks.
 
Pretty much anything other than Garageband will edit down to the sample. For 48k audio that's 1/48000 of a second.
 
Really? I didn't know that was such a common feature. I just use GB cause im so broke.
 
It's impossible to edit a file with any more accuracy than the sample rate. If you record at 48 kHz this would be a 48,000th of a second; if you record at 96kHz sampling you could get this down to a 96,000th of a second.

Unless they exist for scientific purposes, I don't know of any A to D converters that can work at the sort of rates you're asking for.

As others have said, virtually any DAW can get down to sample accuracy though.
 
I just checked. Audacity edits down to the sample level.
 
Why would anyone even need to edit song length down to anything less than a 1 second accuracy anyway?
 
mjbphotos said:
Why would anyone even need to edit song length down to anything less than a 1 second accuracy anyway?
Click to expand...
Well, 1 second is very long. If you're off on an edit by 1 second, or even half of that (500ms), that's a lot. Even 100ms is a lot in the context of music. It's going to be VERY noticeable.
 
Your editing is only as accurate as your sampling rate.

A sampling rate of 192 kHz means that there are 192 samples per millisecond... is 192th of a millisecond accurate enough for you?

Or if you really want to get scientific, I believe the ear can't really hear faster then about 50 milliseconds anyway. If you duplicate a sound and delay it by let's say 35 milliseconds, the ear fuses them together as one sound.
 
SloppyJo said:
Or if you really want to get scientific, I believe the ear can't really hear faster then about 50 milliseconds anyway. If you duplicate a sound and delay it by let's say 35 milliseconds, the ear fuses them together as one sound.
Click to expand...

You can hear way faster than 50ms. The division between hearing two copies of a signal as a phase interaction or as an echo is around 22ms. But for impulses we can hear way smaller time differences than that.
 
bouldersoundguy said:
You can hear way faster than 50ms. The division between hearing two copies of a signal as a phase interaction or as an echo is around 22ms. But for impulses we can hear way smaller time differences than that.
Click to expand...

That was a really rough number; it definitely varies per person. But someone who doesn't do any audio editing or whatnot can't hear as fast as those who are.
 
SloppyJo said:
That was a really rough number; it definitely varies per person. But someone who doesn't do any audio editing or whatnot can't hear as fast as those who are.
Click to expand...

There was a study that showed people (not just sound engineers) could distinguish two impulses much less than a millisecond apart. If I can find it I'll post a link.
 
What it is for:

I need to be able to create blank audio files that are the exact same length as the phrase set on my drum machine and synths arpeggiators. the synth syncs up perfectly with the drum machine because it is running at the same bpm and has the same length of phrase. (2 measures). What i do with the blank audio file that is the same length is loop it on my looping pedal as a kind of "tempo template". That way i can record a phrase with guitar and it will stay in sync.

This has worked well for me in the past for live shows, but anytime i want to loop it for longer time periods it eventually gets out of sync because of those inaccurate millionths of a second.

IE: 2 measures at 175 bpm would be: 2.74285714 seconds.
As far as i know GB will only let me get it as exact as 2.742. Eventually those millionths of a second add up and the loop sounds out of time. (If it runs longer than a few times)

I also have to wonder how accurate my drum machine might be. Alesis sr-16.
 
Anything playing back digital samples (as in short audio clips) will have to round the time of 2 measures @ 175bmp to some number of samples (as in discrete points on the waveform). Different devices may round differently. And even if they all round the same if they aren't all clocked together you'll still get some drift. This isn't an editing problem, it's a hardware problem.
 
douglasfur said:
What it is for:

I need to be able to create blank audio files that are the exact same length as the phrase set on my drum machine and synths arpeggiators. the synth syncs up perfectly with the drum machine because it is running at the same bpm and has the same length of phrase. (2 measures). What i do with the blank audio file that is the same length is loop it on my looping pedal as a kind of "tempo template". That way i can record a phrase with guitar and it will stay in sync.

This has worked well for me in the past for live shows, but anytime i want to loop it for longer time periods it eventually gets out of sync because of those inaccurate millionths of a second.

IE: 2 measures at 175 bpm would be: 2.74285714 seconds.
As far as i know GB will only let me get it as exact as 2.742. Eventually those millionths of a second add up and the loop sounds out of time. (If it runs longer than a few times)

I also have to wonder how accurate my drum machine might be. Alesis sr-16.
Click to expand...

You could ditch the drum machine and use a PC-based beat making solution... but:

(Hint - don't think about doing it for a measure, do it over the whole song length...)

Record your drum machine, analogue wise, not MIDI, into your DAW for a far longer length than the song will ever go live. Insert a MIDI track with a basic beat on it at the same speed alleged BPM as the drum machine is using, then change the BPM on your MIDI track so that, at the end of the song, the last beat on your MIDI track is in the same spot as the last beat on your audio track, or as close as you can get.

Any DAW should give you BPM to 1000th of a beat, and you'll get so close you'll never hear the difference on that last beat.

Chop up your tracks in your DAW as required for your looper. Add salt, pepper and chilli sauce as necessary.

I did this to sync programmed drum tracks on a DAW to recorded-to-click-via-drum-machine tracks on a standalone machine. Works perfectly. I also use a looper, so I know what you're trying to do...
 
You could also send it MIDI Beat Clock from Garage Band. I'm not 100% sure if Garage Band has that, but if it does, you just throw some MIDI cables on the drum looper, set up MIDI Beat Clock, then record the audio coming out of the looper. It'll sync up PERFECTLY to your grid in Garage Band.
 
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