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Re: Calculating Semitones in an octave

From: Andrew Janke
Subject: Re: Calculating Semitones in an octave
Date: Wed, 29 Jan 2020 12:00:37 -0500
User-agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:60.0) Gecko/20100101 Thunderbird/60.9.1

On 1/29/20 11:53 AM, harish3679 wrote:
> Hi guys,
> To find frequency using semitones value from A=440Hz
> We have, f = 2^(n/12)*440 //where n is the semitone value
> Now, to find semitone value for A=432Hz from 440Hz
> It is 432 = 2^(n/12)*440
> I came up with 2^n=0.92668
> Although have no clue how to calculate this in octave rather got an error
> saying
> "2^(n)=0.92668
> parse error:
>   invalid left hand side of assignment"
> Someone, please shed light on this part
> Regards,
> Harish

You can't write arbitrary equations in Octave and have them figure it
out. The "=" sign is an assignment operation, and you need to have a
single variable on the left hand side. So re-work your equation so that
n is by itself on the left hand side.

I think this means taking the base-2 logarithm of both sides, and ending
up with:

n = log2(0.92688)

And that you can run in Octave:

>> log2(0.92668)
ans =   -1.098568597196845e-01


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