Hobbit

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A //hobbit scale// is a generalization of [[MOSScales|MOS]] for arbitrary regular temperaments which is a sort of cousin to [[Dwarves|dwarf scales]]. Given a regular temperament and an equal temperament val v which supports (or belongs to) the temperament, there is a unique scale for the temperament, which can be tuned to any tuning of the temperament, containing v[1] notes to the octave.

==Definition==
To define the hobbit scale we first define a particular [[http://mathworld.wolfram.com/Seminorm.html|seminorm]] on interval space. This seminorm applies to [[Monzos and Interval Space|monzos]] and has the property that the seminorm of a comma of the temperament, or of the unison, the octave and any power of two is 0. It may be defined as follows:

(1) If o = |1 0 0 ... 0> is the monzo for 2 in the [[Harmonic Limit|p-limit]] group.

(2) c1, c2, ..., ci are monzos for a basis for the commas of the temperament.

(3) Form the (i+1)**x**n matrix N = [o, c1, c2, ..., ci] whose rows consist of o and the commas ck.

(4) Monzo weight N by multiplying on the right by a n**x**n diagonal matrix D consisting of log2(qk) along the diagonal, where qk are the primes from 2 to p, obtaining M = ND.

(5) Now find Q = M`M, where M` is the [[RMS tuning|Moore-Penrose pseudoinverse]] of M. On the assumption that the ck form a basis for the commas, then M has linearly independent rows, and by a property of the pseudoinverse, M` = M*(MM*)^(-1), where M* is the transpose of M, so that Q = M*(MM*)^(1)M.

(6) Let P = I - Q, where I is the identity matrix.

(7) For a p-limit monzo or [[Fractional monzos|fractional monzo]] m we now define the seminorm

|| m ||_s = || mDP ||

where the norm on the right is the ordinary Euclidean norm.

(8) If v[1] is odd then for each integer j, 0 less than j less than or equal to v[1], we choose a corresponding monzo mj such that <v|m> = j, 0 less than <J|m> less than or equal to 1 where J is the JI mapping <log2(2) log2(3) ... log2(p)|, and ||m||_s is minimal.

(9) If v[1] is even, we choose a monzo u such that ||u||_s > 0 and ||u||_s is minimal. Then for each integer j, where 0 less than j less than or equal to v[1], we choose a corresponding monzo mj such that <v|m> = j, 0 less than <J|m> less than or equal to 1, and where ||m - u/2||_s is minimal.

(10) We now apply the chosen tuning to the monzos mj, obtaining values (in cents or fractional monzos) defining a scale. The monzos mj are defined only modulo the commas and the octave o, but since the commas are tempered out and mj is in the octave range from 0 less than mj less than or equal to 1200 cents, this does not affect the definition of the scale.

==Example==
For an example, consider the 22 note hobbit for minerva temperament, the 11-limit temperament tempering out 99/98 and 176/175. Here the val is <22 35 51 62 76|, and an interval of minimal nonzero size for the temperament is 16/15, with monzo |4 -1 -1 0 0>. The fractional monzo for half of this, corresponding to the square root, is |4 -1/2 -1/2 0 0>, and intervals representing scale steps are 36/35, 15/14, 11/10, 8/7, 7/6, 40/33, 5/4, 9/7, 4/3, 48/35, 10/7, 22/15, 3/2, 11/7, 8/5, 5/3, 12/7, 7/4, 64/35, 15/8, 64/33, 2/1. A tuning can be defined in various ways, for instance by approximating the above in [[53edo]], or by using the minimax tuning, which has eigenmonzsos 2, 3, and 11.

After applying such a tuning, we discover than there seems to be a certain irregularity or inconsistency in action, in that some of the 11-limit intervals do not stem from the mapping for minerva, but represent additional temperings by 243/242 or 4000/3993. By adding one of these, we can flatten out the irregularity to a corresponding rank two temperament; by adding both, we obtain the rank one temperament with val <65 103 151 183 225|, giving a scale with steps 2433333242432424233333. This sort of thing seems to happen fairly often with hobbit scales.

Original HTML content:

<html><head><title>Hobbits</title></head><body>A <em>hobbit scale</em> is a generalization of <a class="wiki_link" href="/MOSScales">MOS</a> for arbitrary regular temperaments which is a sort of cousin to <a class="wiki_link" href="/Dwarves">dwarf scales</a>. Given a regular temperament and an equal temperament val v which supports (or belongs to) the temperament, there is a unique scale for the temperament, which can be tuned to any tuning of the temperament, containing v[1] notes to the octave.<br />
<br />
<!-- ws:start:WikiTextHeadingRule:0:&lt;h2&gt; --><h2 id="toc0"><a name="x-Definition"></a><!-- ws:end:WikiTextHeadingRule:0 -->Definition</h2>
To define the hobbit scale we first define a particular <a class="wiki_link_ext" href="http://mathworld.wolfram.com/Seminorm.html" rel="nofollow">seminorm</a> on interval space. This seminorm applies to <a class="wiki_link" href="/Monzos%20and%20Interval%20Space">monzos</a> and has the property that the seminorm of a comma of the temperament, or of the unison, the octave and any power of two is 0. It may be defined as follows:<br />
<br />
(1) If o = |1 0 0 ... 0&gt; is the monzo for 2 in the <a class="wiki_link" href="/Harmonic%20Limit">p-limit</a> group.<br />
<br />
(2) c1, c2, ..., ci are monzos for a basis for the commas of the temperament.<br />
<br />
(3) Form the (i+1)<strong>x</strong>n matrix N = [o, c1, c2, ..., ci] whose rows consist of o and the commas ck.<br />
<br />
(4) Monzo weight N by multiplying on the right by a n<strong>x</strong>n diagonal matrix D consisting of log2(qk) along the diagonal, where qk are the primes from 2 to p, obtaining M = ND.<br />
<br />
(5) Now find Q = M`M, where M` is the <a class="wiki_link" href="/RMS%20tuning">Moore-Penrose pseudoinverse</a> of M. On the assumption that the ck form a basis for the commas, then M has linearly independent rows, and by a property of the pseudoinverse, M` = M*(MM*)^(-1), where M* is the transpose of M, so that Q = M*(MM*)^(1)M.<br />
<br />
(6) Let P = I - Q, where I is the identity matrix.<br />
<br />
(7) For a p-limit monzo or <a class="wiki_link" href="/Fractional%20monzos">fractional monzo</a> m we now define the seminorm<br />
<br />


<table class="wiki_table">
    <tr>
        <td>m<br />
</td>
        <td>_s =<br />
</td>
        <td>mDP<br />
</td>
    </tr>
</table>

<br />
where the norm on the right is the ordinary Euclidean norm.<br />
<br />
(8) If v[1] is odd then for each integer j, 0 less than j less than or equal to v[1], we choose a corresponding monzo mj such that &lt;v|m&gt; = j, 0 less than &lt;J|m&gt; less than or equal to 1 where J is the JI mapping &lt;log2(2) log2(3) ... log2(p)|, and ||m||_s is minimal.<br />
<br />
(9) If v[1] is even, we choose a monzo u such that ||u||_s &gt; 0 and ||u||_s is minimal. Then for each integer j, where 0 less than j less than or equal to v[1], we choose a corresponding monzo mj such that &lt;v|m&gt; = j, 0 less than &lt;J|m&gt; less than or equal to 1, and where ||m - u/2||_s is minimal.<br />
<br />
(10) We now apply the chosen tuning to the monzos mj, obtaining values (in cents or fractional monzos) defining a scale. The monzos mj are defined only modulo the commas and the octave o, but since the commas are tempered out and mj is in the octave range from 0 less than mj less than or equal to 1200 cents, this does not affect the definition of the scale.<br />
<br />
<!-- ws:start:WikiTextHeadingRule:2:&lt;h2&gt; --><h2 id="toc1"><a name="x-Example"></a><!-- ws:end:WikiTextHeadingRule:2 -->Example</h2>
For an example, consider the 22 note hobbit for minerva temperament, the 11-limit temperament tempering out 99/98 and 176/175. Here the val is &lt;22 35 51 62 76|, and an interval of minimal nonzero size for the temperament is 16/15, with monzo |4 -1 -1 0 0&gt;. The fractional monzo for half of this, corresponding to the square root, is |4 -1/2 -1/2 0 0&gt;, and intervals representing scale steps are 36/35, 15/14, 11/10, 8/7, 7/6, 40/33, 5/4, 9/7, 4/3, 48/35, 10/7, 22/15, 3/2, 11/7, 8/5, 5/3, 12/7, 7/4, 64/35, 15/8, 64/33, 2/1. A tuning can be defined in various ways, for instance by approximating the above in <a class="wiki_link" href="/53edo">53edo</a>, or by using the minimax tuning, which has eigenmonzsos 2, 3, and 11.<br />
<br />
After applying such a tuning, we discover than there seems to be a certain irregularity or inconsistency in action, in that some of the 11-limit intervals do not stem from the mapping for minerva, but represent additional temperings by 243/242 or 4000/3993. By adding one of these, we can flatten out the irregularity to a corresponding rank two temperament; by adding both, we obtain the rank one temperament with val &lt;65 103 151 183 225|, giving a scale with steps 2433333242432424233333. This sort of thing seems to happen fairly often with hobbit scales.</body></html>