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DaveyNames
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How can I lower the frequency of an audio file?

Oct 8, 2013 10:52 AM

Tags: #lower_frequency

For example in spectral view I can see that the waveforum goes as high as 15,000 Hz. I would like to lower the frequency of the whole file to 10,000 Hz. How can I do that?

 
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  • Currently Being Moderated
    Oct 8, 2013 11:36 PM   in reply to DaveyNames

    I'm a bit confused whether you actually want to lower the frequency (i.e. retune everything lower) or simply filter off frequencies about 10kHz.

     

    If you actually want to change the pitch of your recording, go to Effects/Time and Pitch/Pitch Shifter.  You'll have to work out how much reduction in pitch works for you.

     

    However, if you simply want to remove frequencies above 10k, then that's a job for EQ.  There are lots of different ways to do this but perhaps the easiest would be under Effects/Filter and EQ/Scientific Filter.  On that effect there's a preset called "Hiss Cut (Above 10k)" which will do exactly as you ask without needing to adjust the settings.

     
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  • SteveG(AudioMasters)
    5,602 posts
    Oct 26, 2006
    Currently Being Moderated
    Oct 9, 2013 1:35 AM   in reply to Bob Howes

    I'm a bit confused as to why you'd want to do this at all...

     
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  • Currently Being Moderated
    Oct 9, 2013 3:27 AM   in reply to SteveG(AudioMasters)

    ...because MP3 compression is no longer bad enough for modern ears.  We need another way to mess up recordings completely.

     
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  • Currently Being Moderated
    Oct 9, 2013 4:05 AM   in reply to DaveyNames

    Retuning lower by 30% is definitely NOT what you want either.  That's a HUGE pitch change and it will make your recording sound like the cliche special effect where somebody is shouting "No!" and they slow down time.

     

    You didn't mention you were on CS5.5 before because that is way more limited in terms of the options you have.  From memory, pitch shift was one of the things you don't have.

     

    If it was me, I'd go back to the noise reduction and click remover and experiment with things like the FFT size.  I'd also try doing several pass of light reduction rather than trying to do it all at once.

     
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  • Currently Being Moderated
    Oct 9, 2013 4:20 AM   in reply to Bob Howes

    Just for fun, a quick demo.

     

    I've posted a quick clip, first with the normal frequency range and second pitch shifted by roughly the percentage you want.  It's not pretty.

     

    https://app.box.com/s/tk2flmkr1toxj1iroodw

     
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  • Currently Being Moderated
    Oct 9, 2013 4:37 AM   in reply to DaveyNames

    Okay...terminology time here.

     

    "Lowering the frequency" is shifting the frequency lower like in my silly demo.

     

    What you want it to use a low pass filter (alternately called a high cut filter) to actually remove the unwanted frequencies.  I suspect you'll be happier with the EQ solution if you use a filter with a much steeper cut than the graphic EQ.  The GEQ--especially the ten band version--isn't simply cutting the frequencies about 8k...it's pulling down the preset centre frequencies but, if you could view the result, is pulling down the centre frequencies a lot but leaving some of the sound at frequencies between the presents.

     
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  • Currently Being Moderated
    Oct 9, 2013 5:05 AM   in reply to DaveyNames

    Without having heard your files, I'm suggesting.

     

    First, try the Noise Reduction and the de clicker again--but this time adjust the FFT size (probably bigger) and also do several passes of both effect in succession, rather than trying to do one big pass.

     

    Second, if the NR doesn't work, you'll need to use EQ to remove frequencies about 10k.  However, don't use the ten band Graphic EQ--pick one that allows you to do a very steep cut just over 10k.  The scientific filter I mentioned would be perfect but I honestly can't recall which were there in in 5.5 and which not.  You might do better with the 31 band Graphic or perhaps the parametric (but you'll have to adjust parameters to get what you want.

     
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  • Currently Being Moderated
    Oct 11, 2013 3:05 PM   in reply to DaveyNames

    There is usable audio up to around 13 or 14k, above that there is just shash. Try using the Scientific Filter from the Filter and EQ effects menu. Use the Hiss Cut preset but change the Cutoff from 9998 Hz to 14000Hz. It is pretty horrible over compressed audio though so cannot be improved much.

     
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  • Currently Being Moderated
    Oct 11, 2013 8:53 PM   in reply to DaveyNames

    Having downloaded it I can see the problem with using noise reduction.  The production style is a continuous rush of noise for the whole hour and a half.  (BTW, a 2 or 3 minute sample would have been enough!  Thank goodness for unlimited broadband!)

     

    Anyhow, I had a very quick play and found I like the results best with just some EQ.  Ryclark is right that there's usable audio up to about 13 or 14k but, to my ear, the best compromise is to use the steep Scientific filter at about 11k.  The clarity is instantly improved.  I also worked down the other end and cut the low frequency hash below `100Hz to help the voices stand out.  Finally, I used the 31 band graphic to boost voice frequencies from about 300 to 3000Hz by a couple of dB.

     

    To my ear that sounds pretty good and pulls the voices out of the mire quite well.

     
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  • Currently Being Moderated
    Oct 12, 2013 6:40 AM   in reply to DaveyNames

    Well, because I was experimenting, I did it in 3 passes in Waveform View.  Depending on what you're doing you may choose to set up an effects rack and do real time processing in multitrack.

     

    For my first pass, I used Scientific filter, started with the Hiss Cut (10k) preset but moved the cutoff to 11000.  Other settings were as per the preset.

     

    For my second pass, I changed the Mode to High Pass and the Cutoff to 100Hz.  Other settings the same.

     

    For my third pass I used the 30`band Graphic EQ and started from "Default", i.e. everything flat.  I then pushed the adjustments starting at 250Hz up to 3.2kHz to about +2.5 each--but these numbers are rough--I did it by ear.

     

    I have to stress that this was based on a fairly quick session (and only working with about 3 minutes from the middle which seemed fairly typical.  You may get better results by experimenting more around those settings but at least it's a start.

     
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  • Currently Being Moderated
    Oct 22, 2013 10:07 AM   in reply to DaveyNames

    It didn't re-appear until Audition CC unfortunately. The nearest alternative is the Parametric Equaliser. Click to turn on the HP and LP filters, set the frequencies as Bob's suggestion and set the Slope to 48dB/Oct. You can add the lift from 250 to 3.2k in the Parametric equaliser at the same time.

     
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