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<h2>IMPORTED REVISION FROM WIKISPACES</h2>
An irrational interval or ratio of frequencies given by a real number r has an infinite list of ''nearest just intervals''; if r is rational, the list is finite, terminating in r. For arbitrary (including negative) real numbers this corresponds to what number theorists call ''best rational approximations''. A ratio of integers p/q with q &gt; 0 and p and q relatively prime is a best rational approximation if there is no ratio m/n with n &lt; q which is a better approximation to r. If r is an interval of music it is positive, and both p and q are positive. Note that a nearest just interval is not necessarily nearest in logarithmic terms; 4/3 and 3/2 are the same distance in cents from √2 = 600 cents, but |4/3 - √2| = .08088 whereas |3/2 - √2| = 0.08479, which is larger.
This is an imported revision from Wikispaces. The revision metadata is included below for reference:<br>
: This revision was by author [[User:xenwolf|xenwolf]] and made on <tt>2012-12-12 17:25:20 UTC</tt>.<br>
: The original revision id was <tt>391770730</tt>.<br>
: The revision comment was: <tt>added some links to intervals</tt><br>
The revision contents are below, presented both in the original Wikispaces Wikitext format, and in HTML exactly as Wikispaces rendered it.<br>
<h4>Original Wikitext content:</h4>
<div style="width:100%; max-height:400pt; overflow:auto; background-color:#f8f9fa; border: 1px solid #eaecf0; padding:0em"><pre style="margin:0px;border:none;background:none;word-wrap:break-word;white-space: pre-wrap ! important" class="old-revision-html">An irrational interval or ratio of frequencies given by a real number r has an infinite list of //nearest just intervals//; if r is rational, the list is finite, terminating in r. For arbitrary (including negative) real numbers this corresponds to what number theorists call //best rational approximations//. A ratio of integers p/q with q &gt; 0 and p and q relatively prime is a best rational approximation if there is no ratio m/n with n &lt; q which is a better approximation to r. If r is an interval of music it is positive, and both p and q are positive. Note that a nearest just interval is not necessarily nearest in logarithmic terms; 4/3 and 3/2 are the same distance in cents from √2 = 600 cents, but |4/3 - √2| = .08088 whereas |3/2 - √2| = 0.08479, which is larger.


Best rational approximations also arise in music theory logarithmically, as the best rational approximations to the logarithm base two of some number such as 3/2 or ∜5 is often of interest.
Best rational approximations also arise in music theory logarithmically, as the best rational approximations to the logarithm base two of some number such as 3/2 or ∜5 is often of interest.


The [[http://en.wikipedia.org/wiki/Continued_fraction#Semiconvergents|semiconvergents]] of the continued fraction for r include all of the best rational approximations. The convergents are equivalent with a stronger notion of best approximation, namely [[http://en.wikipedia.org/wiki/Continued_fraction#Best_rational_approximations|best relative approximation]]. Here it is required that |qr - p| is less than |nr - m| for any n &lt; q.
The [http://en.wikipedia.org/wiki/Continued_fraction#Semiconvergents semiconvergents] of the continued fraction for r include all of the best rational approximations. The convergents are equivalent with a stronger notion of best approximation, namely [http://en.wikipedia.org/wiki/Continued_fraction#Best_rational_approximations best relative approximation]. Here it is required that |qr - p| is less than |nr - m| for any n &lt; q.


== Examples ==
== Examples ==
Line 16: Line 9:
=== Approximations for Ratios (of Pure Intervals) ===
=== Approximations for Ratios (of Pure Intervals) ===
The best rational approximations to log2(3/2) define edos which have especially good approximations to the fifth (701.955000865... [[cent|cents]]):
The best rational approximations to log2(3/2) define edos which have especially good approximations to the fifth (701.955000865... [[cent|cents]]):
|| **Step\EDO** || **log([[Tenney Height]])** || **size** in cents || **"error"** in cents ||
|| ... || ... || ... || ... ||
||= 1 \ 1 || 0.0 ||= 1200.0 ||= 498.04 ||
||= 1 \ 2 || 1.0 ||= 600.00 ||= -101.96 ||
||= 2 \ 3 || 2.585 ||= 800.00 ||= 98.045 ||
||= 3 \ [[5edo|5]] || 3.907 ||= 720.00 ||= 18.045 ||
||= 4 \ [[7edo|7]] || 4.807 ||= 685.7143 ||= -16.2407 ||
||= 7 \ [[12edo|12]] || 6.392 ||= 700.00 ||= -1.955 ||
||= 17 \ [[29edo|29]] || 8.945 ||= 703.4483 ||= 1.4933 ||
||= 24 \ [[41edo|41]] || 9.943 ||= 702.43902 ||= 0.48402 ||
||= 31 \ [[53edo|53]] || 10.682 ||= 701.88679 ||= -0.06821 ||


* //for approximations of the harmonic seventh see [[7_4#Approximations]]//
{| class="wikitable"
|-
| | '''Step\EDO'''
| | '''log([[Tenney_Height|Tenney Height]])'''
| | '''size''' in cents
| | '''"error"''' in cents
|-
| | ...
| | ...
| | ...
| | ...
|-
| style="text-align:center;" | 1 \ 1
| | 0.0
| style="text-align:center;" | 1200.0
| style="text-align:center;" | 498.04
|-
| style="text-align:center;" | 1 \ 2
| | 1.0
| style="text-align:center;" | 600.00
| style="text-align:center;" | -101.96
|-
| style="text-align:center;" | 2 \ 3
| | 2.585
| style="text-align:center;" | 800.00
| style="text-align:center;" | 98.045
|-
| style="text-align:center;" | 3 \ [[5edo|5]]
| | 3.907
| style="text-align:center;" | 720.00
| style="text-align:center;" | 18.045
|-
| style="text-align:center;" | 4 \ [[7edo|7]]
| | 4.807
| style="text-align:center;" | 685.7143
| style="text-align:center;" | -16.2407
|-
| style="text-align:center;" | 7 \ [[12edo|12]]
| | 6.392
| style="text-align:center;" | 700.00
| style="text-align:center;" | -1.955
|-
| style="text-align:center;" | 17 \ [[29edo|29]]
| | 8.945
| style="text-align:center;" | 703.4483
| style="text-align:center;" | 1.4933
|-
| style="text-align:center;" | 24 \ [[41edo|41]]
| | 9.943
| style="text-align:center;" | 702.43902
| style="text-align:center;" | 0.48402
|-
| style="text-align:center;" | 31 \ [[53edo|53]]
| | 10.682
| style="text-align:center;" | 701.88679
| style="text-align:center;" | -0.06821
|}
 
<ul><li>''for approximations of the harmonic seventh see [[7/4#Approximations|7_4]]''</li></ul>


=== Approximation for Logarihmic Measures ===
=== Approximation for Logarihmic Measures ===
The 600-cent interval sqrt(2) (6 steps of [[12edo]], "Tritone") approximates following ratios:
The 600-cent interval sqrt(2) (6 steps of [[12edo|12edo]], "Tritone") approximates following ratios:
|| **freq. ratio** || **log2([[Tenney Height]])** || **size** in cents || **"error"** in cents ||
|| ... || ... || ... || ... ||
||= 1 / 1 ||= 0.0 ||= 0.0 ||= 600.0 ||
||= [[3_2|3 / 2]] ||= 2.585 ||= 701.96 ||= 101.96 ||
||= [[4_3|4 / 3]] ||= 3.585 ||= 498.04 ||= -101.96 ||
||= [[7_5|7 / 5]] ||= 5.129 ||= 582.51 ||= -17.49 ||
||= [[17_12|17 / 12]] ||= 7.672 ||= 603.000 ||= 3.000 ||
||= 24 / 17 || ||= 597.000 ||= -3.000 ||
||= 99 / 70 || ||= 600.0883 ||= 0.0883 ||
||= 140 / 99 || ||= 599.9117 ||= -0.0883 ||
|| ... || ... || ... || ... ||
 
The 300-cent interval 2^(1/4) (3 steps of [[12edo]], "minor third") approximates following ratios:
|| **freq. ratio** || **log([[Tenney Height]])** || **size** in cents || **"error"** in cents ||
|| ... || ... || ... || ... ||
||= 1 / 1 ||= 0.0 ||= 0.0 ||= 300.0 ||
||= [[6_5|6 / 5]] ||= 4.907 ||= 315.64 ||= 15.64 ||
||= [[13_11|13 / 11]] ||= 7.160 ||= 289.21 ||= -10.79 ||
||= [[19_16|19 / 16]] ||= 8.248 ||= 297.51 ||= -2.49 ||
||= [[25_21|25 / 21]] ||= 9.036 ||= 301.84 ||= 1.84 ||
|| ... || ... || ... || ... ||
 
</pre></div>
<h4>Original HTML content:</h4>
<div style="width:100%; max-height:400pt; overflow:auto; background-color:#f8f9fa; border: 1px solid #eaecf0; padding:0em"><pre style="margin:0px;border:none;background:none;word-wrap:break-word;width:200%;white-space: pre-wrap ! important" class="old-revision-html">&lt;html&gt;&lt;head&gt;&lt;title&gt;Nearest just interval&lt;/title&gt;&lt;/head&gt;&lt;body&gt;An irrational interval or ratio of frequencies given by a real number r has an infinite list of &lt;em&gt;nearest just intervals&lt;/em&gt;; if r is rational, the list is finite, terminating in r. For arbitrary (including negative) real numbers this corresponds to what number theorists call &lt;em&gt;best rational approximations&lt;/em&gt;. A ratio of integers p/q with q &amp;gt; 0 and p and q relatively prime is a best rational approximation if there is no ratio m/n with n &amp;lt; q which is a better approximation to r. If r is an interval of music it is positive, and both p and q are positive. Note that a nearest just interval is not necessarily nearest in logarithmic terms; 4/3 and 3/2 are the same distance in cents from √2 = 600 cents, but |4/3 - √2| = .08088 whereas |3/2 - √2| = 0.08479, which is larger.&lt;br /&gt;
&lt;br /&gt;
Best rational approximations also arise in music theory logarithmically, as the best rational approximations to the logarithm base two of some number such as 3/2 or ∜5 is often of interest.&lt;br /&gt;
&lt;br /&gt;
The &lt;a class="wiki_link_ext" href="http://en.wikipedia.org/wiki/Continued_fraction#Semiconvergents" rel="nofollow"&gt;semiconvergents&lt;/a&gt; of the continued fraction for r include all of the best rational approximations. The convergents are equivalent with a stronger notion of best approximation, namely &lt;a class="wiki_link_ext" href="http://en.wikipedia.org/wiki/Continued_fraction#Best_rational_approximations" rel="nofollow"&gt;best relative approximation&lt;/a&gt;. Here it is required that |qr - p| is less than |nr - m| for any n &amp;lt; q.&lt;br /&gt;
&lt;br /&gt;
&lt;!-- ws:start:WikiTextHeadingRule:0:&amp;lt;h2&amp;gt; --&gt;&lt;h2 id="toc0"&gt;&lt;a name="x-Examples"&gt;&lt;/a&gt;&lt;!-- ws:end:WikiTextHeadingRule:0 --&gt; Examples &lt;/h2&gt;
&lt;br /&gt;
&lt;!-- ws:start:WikiTextHeadingRule:2:&amp;lt;h3&amp;gt; --&gt;&lt;h3 id="toc1"&gt;&lt;a name="x-Examples-Approximations for Ratios (of Pure Intervals)"&gt;&lt;/a&gt;&lt;!-- ws:end:WikiTextHeadingRule:2 --&gt; Approximations for Ratios (of Pure Intervals) &lt;/h3&gt;
The best rational approximations to log2(3/2) define edos which have especially good approximations to the fifth (701.955000865... &lt;a class="wiki_link" href="/cent"&gt;cents&lt;/a&gt;):&lt;br /&gt;
 
 
&lt;table class="wiki_table"&gt;
    &lt;tr&gt;
        &lt;td&gt;&lt;strong&gt;Step\EDO&lt;/strong&gt;&lt;br /&gt;
&lt;/td&gt;
        &lt;td&gt;&lt;strong&gt;log(&lt;a class="wiki_link" href="/Tenney%20Height"&gt;Tenney Height&lt;/a&gt;)&lt;/strong&gt;&lt;br /&gt;
&lt;/td&gt;
        &lt;td&gt;&lt;strong&gt;size&lt;/strong&gt; in cents&lt;br /&gt;
&lt;/td&gt;
        &lt;td&gt;&lt;strong&gt;&amp;quot;error&amp;quot;&lt;/strong&gt; in cents&lt;br /&gt;
&lt;/td&gt;
    &lt;/tr&gt;
    &lt;tr&gt;
        &lt;td&gt;...&lt;br /&gt;
&lt;/td&gt;
        &lt;td&gt;...&lt;br /&gt;
&lt;/td&gt;
        &lt;td&gt;...&lt;br /&gt;
&lt;/td&gt;
        &lt;td&gt;...&lt;br /&gt;
&lt;/td&gt;
    &lt;/tr&gt;
    &lt;tr&gt;
        &lt;td style="text-align: center;"&gt;1 \ 1&lt;br /&gt;
&lt;/td&gt;
        &lt;td&gt;0.0&lt;br /&gt;
&lt;/td&gt;
        &lt;td style="text-align: center;"&gt;1200.0&lt;br /&gt;
&lt;/td&gt;
        &lt;td style="text-align: center;"&gt;498.04&lt;br /&gt;
&lt;/td&gt;
    &lt;/tr&gt;
    &lt;tr&gt;
        &lt;td style="text-align: center;"&gt;1 \ 2&lt;br /&gt;
&lt;/td&gt;
        &lt;td&gt;1.0&lt;br /&gt;
&lt;/td&gt;
        &lt;td style="text-align: center;"&gt;600.00&lt;br /&gt;
&lt;/td&gt;
        &lt;td style="text-align: center;"&gt;-101.96&lt;br /&gt;
&lt;/td&gt;
    &lt;/tr&gt;
    &lt;tr&gt;
        &lt;td style="text-align: center;"&gt;2 \ 3&lt;br /&gt;
&lt;/td&gt;
        &lt;td&gt;2.585&lt;br /&gt;
&lt;/td&gt;
        &lt;td style="text-align: center;"&gt;800.00&lt;br /&gt;
&lt;/td&gt;
        &lt;td style="text-align: center;"&gt;98.045&lt;br /&gt;
&lt;/td&gt;
    &lt;/tr&gt;
    &lt;tr&gt;
        &lt;td style="text-align: center;"&gt;3 \ &lt;a class="wiki_link" href="/5edo"&gt;5&lt;/a&gt;&lt;br /&gt;
&lt;/td&gt;
        &lt;td&gt;3.907&lt;br /&gt;
&lt;/td&gt;
        &lt;td style="text-align: center;"&gt;720.00&lt;br /&gt;
&lt;/td&gt;
        &lt;td style="text-align: center;"&gt;18.045&lt;br /&gt;
&lt;/td&gt;
    &lt;/tr&gt;
    &lt;tr&gt;
        &lt;td style="text-align: center;"&gt;4 \ &lt;a class="wiki_link" href="/7edo"&gt;7&lt;/a&gt;&lt;br /&gt;
&lt;/td&gt;
        &lt;td&gt;4.807&lt;br /&gt;
&lt;/td&gt;
        &lt;td style="text-align: center;"&gt;685.7143&lt;br /&gt;
&lt;/td&gt;
        &lt;td style="text-align: center;"&gt;-16.2407&lt;br /&gt;
&lt;/td&gt;
    &lt;/tr&gt;
    &lt;tr&gt;
        &lt;td style="text-align: center;"&gt;7 \ &lt;a class="wiki_link" href="/12edo"&gt;12&lt;/a&gt;&lt;br /&gt;
&lt;/td&gt;
        &lt;td&gt;6.392&lt;br /&gt;
&lt;/td&gt;
        &lt;td style="text-align: center;"&gt;700.00&lt;br /&gt;
&lt;/td&gt;
        &lt;td style="text-align: center;"&gt;-1.955&lt;br /&gt;
&lt;/td&gt;
    &lt;/tr&gt;
    &lt;tr&gt;
        &lt;td style="text-align: center;"&gt;17 \ &lt;a class="wiki_link" href="/29edo"&gt;29&lt;/a&gt;&lt;br /&gt;
&lt;/td&gt;
        &lt;td&gt;8.945&lt;br /&gt;
&lt;/td&gt;
        &lt;td style="text-align: center;"&gt;703.4483&lt;br /&gt;
&lt;/td&gt;
        &lt;td style="text-align: center;"&gt;1.4933&lt;br /&gt;
&lt;/td&gt;
    &lt;/tr&gt;
    &lt;tr&gt;
        &lt;td style="text-align: center;"&gt;24 \ &lt;a class="wiki_link" href="/41edo"&gt;41&lt;/a&gt;&lt;br /&gt;
&lt;/td&gt;
        &lt;td&gt;9.943&lt;br /&gt;
&lt;/td&gt;
        &lt;td style="text-align: center;"&gt;702.43902&lt;br /&gt;
&lt;/td&gt;
        &lt;td style="text-align: center;"&gt;0.48402&lt;br /&gt;
&lt;/td&gt;
    &lt;/tr&gt;
    &lt;tr&gt;
        &lt;td style="text-align: center;"&gt;31 \ &lt;a class="wiki_link" href="/53edo"&gt;53&lt;/a&gt;&lt;br /&gt;
&lt;/td&gt;
        &lt;td&gt;10.682&lt;br /&gt;
&lt;/td&gt;
        &lt;td style="text-align: center;"&gt;701.88679&lt;br /&gt;
&lt;/td&gt;
        &lt;td style="text-align: center;"&gt;-0.06821&lt;br /&gt;
&lt;/td&gt;
    &lt;/tr&gt;
&lt;/table&gt;
 
&lt;br /&gt;
&lt;ul&gt;&lt;li&gt;&lt;em&gt;for approximations of the harmonic seventh see &lt;a class="wiki_link" href="/7_4#Approximations"&gt;7_4&lt;/a&gt;&lt;/em&gt;&lt;/li&gt;&lt;/ul&gt;&lt;br /&gt;
&lt;!-- ws:start:WikiTextHeadingRule:4:&amp;lt;h3&amp;gt; --&gt;&lt;h3 id="toc2"&gt;&lt;a name="x-Examples-Approximation for Logarihmic Measures"&gt;&lt;/a&gt;&lt;!-- ws:end:WikiTextHeadingRule:4 --&gt; Approximation for Logarihmic Measures &lt;/h3&gt;
The 600-cent interval sqrt(2) (6 steps of &lt;a class="wiki_link" href="/12edo"&gt;12edo&lt;/a&gt;, &amp;quot;Tritone&amp;quot;) approximates following ratios:&lt;br /&gt;
 
 
&lt;table class="wiki_table"&gt;
    &lt;tr&gt;
        &lt;td&gt;&lt;strong&gt;freq. ratio&lt;/strong&gt;&lt;br /&gt;
&lt;/td&gt;
        &lt;td&gt;&lt;strong&gt;log2(&lt;a class="wiki_link" href="/Tenney%20Height"&gt;Tenney Height&lt;/a&gt;)&lt;/strong&gt;&lt;br /&gt;
&lt;/td&gt;
        &lt;td&gt;&lt;strong&gt;size&lt;/strong&gt; in cents&lt;br /&gt;
&lt;/td&gt;
        &lt;td&gt;&lt;strong&gt;&amp;quot;error&amp;quot;&lt;/strong&gt; in cents&lt;br /&gt;
&lt;/td&gt;
    &lt;/tr&gt;
    &lt;tr&gt;
        &lt;td&gt;...&lt;br /&gt;
&lt;/td&gt;
        &lt;td&gt;...&lt;br /&gt;
&lt;/td&gt;
        &lt;td&gt;...&lt;br /&gt;
&lt;/td&gt;
        &lt;td&gt;...&lt;br /&gt;
&lt;/td&gt;
    &lt;/tr&gt;
    &lt;tr&gt;
        &lt;td style="text-align: center;"&gt;1 / 1&lt;br /&gt;
&lt;/td&gt;
        &lt;td style="text-align: center;"&gt;0.0&lt;br /&gt;
&lt;/td&gt;
        &lt;td style="text-align: center;"&gt;0.0&lt;br /&gt;
&lt;/td&gt;
        &lt;td style="text-align: center;"&gt;600.0&lt;br /&gt;
&lt;/td&gt;
    &lt;/tr&gt;
    &lt;tr&gt;
        &lt;td style="text-align: center;"&gt;&lt;a class="wiki_link" href="/3_2"&gt;3 / 2&lt;/a&gt;&lt;br /&gt;
&lt;/td&gt;
        &lt;td style="text-align: center;"&gt;2.585&lt;br /&gt;
&lt;/td&gt;
        &lt;td style="text-align: center;"&gt;701.96&lt;br /&gt;
&lt;/td&gt;
        &lt;td style="text-align: center;"&gt;101.96&lt;br /&gt;
&lt;/td&gt;
    &lt;/tr&gt;
    &lt;tr&gt;
        &lt;td style="text-align: center;"&gt;&lt;a class="wiki_link" href="/4_3"&gt;4 / 3&lt;/a&gt;&lt;br /&gt;
&lt;/td&gt;
        &lt;td style="text-align: center;"&gt;3.585&lt;br /&gt;
&lt;/td&gt;
        &lt;td style="text-align: center;"&gt;498.04&lt;br /&gt;
&lt;/td&gt;
        &lt;td style="text-align: center;"&gt;-101.96&lt;br /&gt;
&lt;/td&gt;
    &lt;/tr&gt;
    &lt;tr&gt;
        &lt;td style="text-align: center;"&gt;&lt;a class="wiki_link" href="/7_5"&gt;7 / 5&lt;/a&gt;&lt;br /&gt;
&lt;/td&gt;
        &lt;td style="text-align: center;"&gt;5.129&lt;br /&gt;
&lt;/td&gt;
        &lt;td style="text-align: center;"&gt;582.51&lt;br /&gt;
&lt;/td&gt;
        &lt;td style="text-align: center;"&gt;-17.49&lt;br /&gt;
&lt;/td&gt;
    &lt;/tr&gt;
    &lt;tr&gt;
        &lt;td style="text-align: center;"&gt;&lt;a class="wiki_link" href="/17_12"&gt;17 / 12&lt;/a&gt;&lt;br /&gt;
&lt;/td&gt;
        &lt;td style="text-align: center;"&gt;7.672&lt;br /&gt;
&lt;/td&gt;
        &lt;td style="text-align: center;"&gt;603.000&lt;br /&gt;
&lt;/td&gt;
        &lt;td style="text-align: center;"&gt;3.000&lt;br /&gt;
&lt;/td&gt;
    &lt;/tr&gt;
    &lt;tr&gt;
        &lt;td style="text-align: center;"&gt;24 / 17&lt;br /&gt;
&lt;/td&gt;
        &lt;td&gt;&lt;br /&gt;
&lt;/td&gt;
        &lt;td style="text-align: center;"&gt;597.000&lt;br /&gt;
&lt;/td&gt;
        &lt;td style="text-align: center;"&gt;-3.000&lt;br /&gt;
&lt;/td&gt;
    &lt;/tr&gt;
    &lt;tr&gt;
        &lt;td style="text-align: center;"&gt;99 / 70&lt;br /&gt;
&lt;/td&gt;
        &lt;td&gt;&lt;br /&gt;
&lt;/td&gt;
        &lt;td style="text-align: center;"&gt;600.0883&lt;br /&gt;
&lt;/td&gt;
        &lt;td style="text-align: center;"&gt;0.0883&lt;br /&gt;
&lt;/td&gt;
    &lt;/tr&gt;
    &lt;tr&gt;
        &lt;td style="text-align: center;"&gt;140 / 99&lt;br /&gt;
&lt;/td&gt;
        &lt;td&gt;&lt;br /&gt;
&lt;/td&gt;
        &lt;td style="text-align: center;"&gt;599.9117&lt;br /&gt;
&lt;/td&gt;
        &lt;td style="text-align: center;"&gt;-0.0883&lt;br /&gt;
&lt;/td&gt;
    &lt;/tr&gt;
    &lt;tr&gt;
        &lt;td&gt;...&lt;br /&gt;
&lt;/td&gt;
        &lt;td&gt;...&lt;br /&gt;
&lt;/td&gt;
        &lt;td&gt;...&lt;br /&gt;
&lt;/td&gt;
        &lt;td&gt;...&lt;br /&gt;
&lt;/td&gt;
    &lt;/tr&gt;
&lt;/table&gt;
 
&lt;br /&gt;
The 300-cent interval 2^(1/4) (3 steps of &lt;a class="wiki_link" href="/12edo"&gt;12edo&lt;/a&gt;, &amp;quot;minor third&amp;quot;) approximates following ratios:&lt;br /&gt;


{| class="wikitable"
|-
| | '''freq. ratio'''
| | '''log2([[Tenney_Height|Tenney Height]])'''
| | '''size''' in cents
| | '''"error"''' in cents
|-
| | ...
| | ...
| | ...
| | ...
|-
| style="text-align:center;" | 1 / 1
| style="text-align:center;" | 0.0
| style="text-align:center;" | 0.0
| style="text-align:center;" | 600.0
|-
| style="text-align:center;" | [[3/2|3 / 2]]
| style="text-align:center;" | 2.585
| style="text-align:center;" | 701.96
| style="text-align:center;" | 101.96
|-
| style="text-align:center;" | [[4/3|4 / 3]]
| style="text-align:center;" | 3.585
| style="text-align:center;" | 498.04
| style="text-align:center;" | -101.96
|-
| style="text-align:center;" | [[7/5|7 / 5]]
| style="text-align:center;" | 5.129
| style="text-align:center;" | 582.51
| style="text-align:center;" | -17.49
|-
| style="text-align:center;" | [[17/12|17 / 12]]
| style="text-align:center;" | 7.672
| style="text-align:center;" | 603.000
| style="text-align:center;" | 3.000
|-
| style="text-align:center;" | 24 / 17
| |
| style="text-align:center;" | 597.000
| style="text-align:center;" | -3.000
|-
| style="text-align:center;" | 99 / 70
| |
| style="text-align:center;" | 600.0883
| style="text-align:center;" | 0.0883
|-
| style="text-align:center;" | 140 / 99
| |
| style="text-align:center;" | 599.9117
| style="text-align:center;" | -0.0883
|-
| | ...
| | ...
| | ...
| | ...
|}


&lt;table class="wiki_table"&gt;
The 300-cent interval 2^(1/4) (3 steps of [[12edo|12edo]], "minor third") approximates following ratios:
    &lt;tr&gt;
        &lt;td&gt;&lt;strong&gt;freq. ratio&lt;/strong&gt;&lt;br /&gt;
&lt;/td&gt;
        &lt;td&gt;&lt;strong&gt;log(&lt;a class="wiki_link" href="/Tenney%20Height"&gt;Tenney Height&lt;/a&gt;)&lt;/strong&gt;&lt;br /&gt;
&lt;/td&gt;
        &lt;td&gt;&lt;strong&gt;size&lt;/strong&gt; in cents&lt;br /&gt;
&lt;/td&gt;
        &lt;td&gt;&lt;strong&gt;&amp;quot;error&amp;quot;&lt;/strong&gt; in cents&lt;br /&gt;
&lt;/td&gt;
    &lt;/tr&gt;
    &lt;tr&gt;
        &lt;td&gt;...&lt;br /&gt;
&lt;/td&gt;
        &lt;td&gt;...&lt;br /&gt;
&lt;/td&gt;
        &lt;td&gt;...&lt;br /&gt;
&lt;/td&gt;
        &lt;td&gt;...&lt;br /&gt;
&lt;/td&gt;
    &lt;/tr&gt;
    &lt;tr&gt;
        &lt;td style="text-align: center;"&gt;1 / 1&lt;br /&gt;
&lt;/td&gt;
        &lt;td style="text-align: center;"&gt;0.0&lt;br /&gt;
&lt;/td&gt;
        &lt;td style="text-align: center;"&gt;0.0&lt;br /&gt;
&lt;/td&gt;
        &lt;td style="text-align: center;"&gt;300.0&lt;br /&gt;
&lt;/td&gt;
    &lt;/tr&gt;
    &lt;tr&gt;
        &lt;td style="text-align: center;"&gt;&lt;a class="wiki_link" href="/6_5"&gt;6 / 5&lt;/a&gt;&lt;br /&gt;
&lt;/td&gt;
        &lt;td style="text-align: center;"&gt;4.907&lt;br /&gt;
&lt;/td&gt;
        &lt;td style="text-align: center;"&gt;315.64&lt;br /&gt;
&lt;/td&gt;
        &lt;td style="text-align: center;"&gt;15.64&lt;br /&gt;
&lt;/td&gt;
    &lt;/tr&gt;
    &lt;tr&gt;
        &lt;td style="text-align: center;"&gt;&lt;a class="wiki_link" href="/13_11"&gt;13 / 11&lt;/a&gt;&lt;br /&gt;
&lt;/td&gt;
        &lt;td style="text-align: center;"&gt;7.160&lt;br /&gt;
&lt;/td&gt;
        &lt;td style="text-align: center;"&gt;289.21&lt;br /&gt;
&lt;/td&gt;
        &lt;td style="text-align: center;"&gt;-10.79&lt;br /&gt;
&lt;/td&gt;
    &lt;/tr&gt;
    &lt;tr&gt;
        &lt;td style="text-align: center;"&gt;&lt;a class="wiki_link" href="/19_16"&gt;19 / 16&lt;/a&gt;&lt;br /&gt;
&lt;/td&gt;
        &lt;td style="text-align: center;"&gt;8.248&lt;br /&gt;
&lt;/td&gt;
        &lt;td style="text-align: center;"&gt;297.51&lt;br /&gt;
&lt;/td&gt;
        &lt;td style="text-align: center;"&gt;-2.49&lt;br /&gt;
&lt;/td&gt;
    &lt;/tr&gt;
    &lt;tr&gt;
        &lt;td style="text-align: center;"&gt;&lt;a class="wiki_link" href="/25_21"&gt;25 / 21&lt;/a&gt;&lt;br /&gt;
&lt;/td&gt;
        &lt;td style="text-align: center;"&gt;9.036&lt;br /&gt;
&lt;/td&gt;
        &lt;td style="text-align: center;"&gt;301.84&lt;br /&gt;
&lt;/td&gt;
        &lt;td style="text-align: center;"&gt;1.84&lt;br /&gt;
&lt;/td&gt;
    &lt;/tr&gt;
    &lt;tr&gt;
        &lt;td&gt;...&lt;br /&gt;
&lt;/td&gt;
        &lt;td&gt;...&lt;br /&gt;
&lt;/td&gt;
        &lt;td&gt;...&lt;br /&gt;
&lt;/td&gt;
        &lt;td&gt;...&lt;br /&gt;
&lt;/td&gt;
    &lt;/tr&gt;
&lt;/table&gt;


&lt;/body&gt;&lt;/html&gt;</pre></div>
{| class="wikitable"
|-
| | '''freq. ratio'''
| | '''log([[Tenney_Height|Tenney Height]])'''
| | '''size''' in cents
| | '''"error"''' in cents
|-
| | ...
| | ...
| | ...
| | ...
|-
| style="text-align:center;" | 1 / 1
| style="text-align:center;" | 0.0
| style="text-align:center;" | 0.0
| style="text-align:center;" | 300.0
|-
| style="text-align:center;" | [[6/5|6 / 5]]
| style="text-align:center;" | 4.907
| style="text-align:center;" | 315.64
| style="text-align:center;" | 15.64
|-
| style="text-align:center;" | [[13/11|13 / 11]]
| style="text-align:center;" | 7.160
| style="text-align:center;" | 289.21
| style="text-align:center;" | -10.79
|-
| style="text-align:center;" | [[19/16|19 / 16]]
| style="text-align:center;" | 8.248
| style="text-align:center;" | 297.51
| style="text-align:center;" | -2.49
|-
| style="text-align:center;" | [[25/21|25 / 21]]
| style="text-align:center;" | 9.036
| style="text-align:center;" | 301.84
| style="text-align:center;" | 1.84
|-
| | ...
| | ...
| | ...
| | ...
|}
[[Category:approximation]]
[[Category:hack]]
[[Category:just]]
[[Category:math]]
[[Category:theory]]
[[Category:todo:add_examples]]

Revision as of 00:00, 17 July 2018

An irrational interval or ratio of frequencies given by a real number r has an infinite list of nearest just intervals; if r is rational, the list is finite, terminating in r. For arbitrary (including negative) real numbers this corresponds to what number theorists call best rational approximations. A ratio of integers p/q with q > 0 and p and q relatively prime is a best rational approximation if there is no ratio m/n with n < q which is a better approximation to r. If r is an interval of music it is positive, and both p and q are positive. Note that a nearest just interval is not necessarily nearest in logarithmic terms; 4/3 and 3/2 are the same distance in cents from √2 = 600 cents, but |4/3 - √2| = .08088 whereas |3/2 - √2| = 0.08479, which is larger.

Best rational approximations also arise in music theory logarithmically, as the best rational approximations to the logarithm base two of some number such as 3/2 or ∜5 is often of interest.

The semiconvergents of the continued fraction for r include all of the best rational approximations. The convergents are equivalent with a stronger notion of best approximation, namely best relative approximation. Here it is required that |qr - p| is less than |nr - m| for any n < q.

Examples

Approximations for Ratios (of Pure Intervals)

The best rational approximations to log2(3/2) define edos which have especially good approximations to the fifth (701.955000865... cents):

Step\EDO log(Tenney Height) size in cents "error" in cents
... ... ... ...
1 \ 1 0.0 1200.0 498.04
1 \ 2 1.0 600.00 -101.96
2 \ 3 2.585 800.00 98.045
3 \ 5 3.907 720.00 18.045
4 \ 7 4.807 685.7143 -16.2407
7 \ 12 6.392 700.00 -1.955
17 \ 29 8.945 703.4483 1.4933
24 \ 41 9.943 702.43902 0.48402
31 \ 53 10.682 701.88679 -0.06821
  • for approximations of the harmonic seventh see 7_4

Approximation for Logarihmic Measures

The 600-cent interval sqrt(2) (6 steps of 12edo, "Tritone") approximates following ratios:

freq. ratio log2(Tenney Height) size in cents "error" in cents
... ... ... ...
1 / 1 0.0 0.0 600.0
3 / 2 2.585 701.96 101.96
4 / 3 3.585 498.04 -101.96
7 / 5 5.129 582.51 -17.49
17 / 12 7.672 603.000 3.000
24 / 17 597.000 -3.000
99 / 70 600.0883 0.0883
140 / 99 599.9117 -0.0883
... ... ... ...

The 300-cent interval 2^(1/4) (3 steps of 12edo, "minor third") approximates following ratios:

freq. ratio log(Tenney Height) size in cents "error" in cents
... ... ... ...
1 / 1 0.0 0.0 300.0
6 / 5 4.907 315.64 15.64
13 / 11 7.160 289.21 -10.79
19 / 16 8.248 297.51 -2.49
25 / 21 9.036 301.84 1.84
... ... ... ...