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  182.   <section id="module-audioop">

  183. <span id="audioop-manipulate-raw-audio-data"></span><h1><a class="reference internal" href="#module-audioop" title="audioop: Manipulate raw audio data. (deprecated)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">audioop</span></code></a> — Manipulate raw audio data<a class="headerlink" href="#module-audioop" title="Link to this heading">¶</a></h1>

  184. <div class="deprecated-removed">

  185. <p><span class="versionmodified">Deprecated since version 3.11, will be removed in version 3.13: </span>The <a class="reference internal" href="#module-audioop" title="audioop: Manipulate raw audio data. (deprecated)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">audioop</span></code></a> module is deprecated

  186. (see <span class="target" id="index-0"></span><a class="pep reference external" href="https://peps.python.org/pep-0594/#audioop"><strong>PEP 594</strong></a> for details).</p>

  187. </div>

  188. <hr class="docutils" />

  189. <p>The <a class="reference internal" href="#module-audioop" title="audioop: Manipulate raw audio data. (deprecated)"><code class="xref py py-mod docutils literal notranslate"><span class="pre">audioop</span></code></a> module contains some useful operations on sound fragments.

  190. It operates on sound fragments consisting of signed integer samples 8, 16, 24

  191. or 32 bits wide, stored in <a class="reference internal" href="../glossary.html#term-bytes-like-object"><span class="xref std std-term">bytes-like objects</span></a>.  All scalar items are

  192. integers, unless specified otherwise.</p>

  193. <div class="versionchanged">

  194. <p><span class="versionmodified changed">Changed in version 3.4: </span>Support for 24-bit samples was added.

  195. All functions now accept any <a class="reference internal" href="../glossary.html#term-bytes-like-object"><span class="xref std std-term">bytes-like object</span></a>.

  196. String input now results in an immediate error.</p>

  197. </div>

  198. <p id="index-1">This module provides support for a-LAW, u-LAW and Intel/DVI ADPCM encodings.</p>

  199. <p>A few of the more complicated operations only take 16-bit samples, otherwise the

  200. sample size (in bytes) is always a parameter of the operation.</p>

  201. <p>The module defines the following variables and functions:</p>

  202. <dl class="py exception">

  203. <dt class="sig sig-object py" id="audioop.error">

  204. <em class="property"><span class="pre">exception</span><span class="w"> </span></em><span class="sig-prename descclassname"><span class="pre">audioop.</span></span><span class="sig-name descname"><span class="pre">error</span></span><a class="headerlink" href="#audioop.error" title="Link to this definition">¶</a></dt>

  205. <dd><p>This exception is raised on all errors, such as unknown number of bytes per

  206. sample, etc.</p>

  207. </dd></dl>

  208. 

  209. <dl class="py function">

  210. <dt class="sig sig-object py" id="audioop.add">

  211. <span class="sig-prename descclassname"><span class="pre">audioop.</span></span><span class="sig-name descname"><span class="pre">add</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">fragment1</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">fragment2</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">width</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#audioop.add" title="Link to this definition">¶</a></dt>

  212. <dd><p>Return a fragment which is the addition of the two samples passed as parameters.

  213. <em>width</em> is the sample width in bytes, either <code class="docutils literal notranslate"><span class="pre">1</span></code>, <code class="docutils literal notranslate"><span class="pre">2</span></code>, <code class="docutils literal notranslate"><span class="pre">3</span></code> or <code class="docutils literal notranslate"><span class="pre">4</span></code>.  Both

  214. fragments should have the same length.  Samples are truncated in case of overflow.</p>

  215. </dd></dl>

  216. 

  217. <dl class="py function">

  218. <dt class="sig sig-object py" id="audioop.adpcm2lin">

  219. <span class="sig-prename descclassname"><span class="pre">audioop.</span></span><span class="sig-name descname"><span class="pre">adpcm2lin</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">adpcmfragment</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">width</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">state</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#audioop.adpcm2lin" title="Link to this definition">¶</a></dt>

  220. <dd><p>Decode an Intel/DVI ADPCM coded fragment to a linear fragment.  See the

  221. description of <a class="reference internal" href="#audioop.lin2adpcm" title="audioop.lin2adpcm"><code class="xref py py-func docutils literal notranslate"><span class="pre">lin2adpcm()</span></code></a> for details on ADPCM coding. Return a tuple

  222. <code class="docutils literal notranslate"><span class="pre">(sample,</span> <span class="pre">newstate)</span></code> where the sample has the width specified in <em>width</em>.</p>

  223. </dd></dl>

  224. 

  225. <dl class="py function">

  226. <dt class="sig sig-object py" id="audioop.alaw2lin">

  227. <span class="sig-prename descclassname"><span class="pre">audioop.</span></span><span class="sig-name descname"><span class="pre">alaw2lin</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">fragment</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">width</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#audioop.alaw2lin" title="Link to this definition">¶</a></dt>

  228. <dd><p>Convert sound fragments in a-LAW encoding to linearly encoded sound fragments.

  229. a-LAW encoding always uses 8 bits samples, so <em>width</em> refers only to the sample

  230. width of the output fragment here.</p>

  231. </dd></dl>

  232. 

  233. <dl class="py function">

  234. <dt class="sig sig-object py" id="audioop.avg">

  235. <span class="sig-prename descclassname"><span class="pre">audioop.</span></span><span class="sig-name descname"><span class="pre">avg</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">fragment</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">width</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#audioop.avg" title="Link to this definition">¶</a></dt>

  236. <dd><p>Return the average over all samples in the fragment.</p>

  237. </dd></dl>

  238. 

  239. <dl class="py function">

  240. <dt class="sig sig-object py" id="audioop.avgpp">

  241. <span class="sig-prename descclassname"><span class="pre">audioop.</span></span><span class="sig-name descname"><span class="pre">avgpp</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">fragment</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">width</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#audioop.avgpp" title="Link to this definition">¶</a></dt>

  242. <dd><p>Return the average peak-peak value over all samples in the fragment. No

  243. filtering is done, so the usefulness of this routine is questionable.</p>

  244. </dd></dl>

  245. 

  246. <dl class="py function">

  247. <dt class="sig sig-object py" id="audioop.bias">

  248. <span class="sig-prename descclassname"><span class="pre">audioop.</span></span><span class="sig-name descname"><span class="pre">bias</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">fragment</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">width</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">bias</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#audioop.bias" title="Link to this definition">¶</a></dt>

  249. <dd><p>Return a fragment that is the original fragment with a bias added to each

  250. sample.  Samples wrap around in case of overflow.</p>

  251. </dd></dl>

  252. 

  253. <dl class="py function">

  254. <dt class="sig sig-object py" id="audioop.byteswap">

  255. <span class="sig-prename descclassname"><span class="pre">audioop.</span></span><span class="sig-name descname"><span class="pre">byteswap</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">fragment</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">width</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#audioop.byteswap" title="Link to this definition">¶</a></dt>

  256. <dd><p>“Byteswap” all samples in a fragment and returns the modified fragment.

  257. Converts big-endian samples to little-endian and vice versa.</p>

  258. <div class="versionadded">

  259. <p><span class="versionmodified added">New in version 3.4.</span></p>

  260. </div>

  261. </dd></dl>

  262. 

  263. <dl class="py function">

  264. <dt class="sig sig-object py" id="audioop.cross">

  265. <span class="sig-prename descclassname"><span class="pre">audioop.</span></span><span class="sig-name descname"><span class="pre">cross</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">fragment</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">width</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#audioop.cross" title="Link to this definition">¶</a></dt>

  266. <dd><p>Return the number of zero crossings in the fragment passed as an argument.</p>

  267. </dd></dl>

  268. 

  269. <dl class="py function">

  270. <dt class="sig sig-object py" id="audioop.findfactor">

  271. <span class="sig-prename descclassname"><span class="pre">audioop.</span></span><span class="sig-name descname"><span class="pre">findfactor</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">fragment</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">reference</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#audioop.findfactor" title="Link to this definition">¶</a></dt>

  272. <dd><p>Return a factor <em>F</em> such that <code class="docutils literal notranslate"><span class="pre">rms(add(fragment,</span> <span class="pre">mul(reference,</span> <span class="pre">-F)))</span></code> is

  273. minimal, i.e., return the factor with which you should multiply <em>reference</em> to

  274. make it match as well as possible to <em>fragment</em>.  The fragments should both

  275. contain 2-byte samples.</p>

  276. <p>The time taken by this routine is proportional to <code class="docutils literal notranslate"><span class="pre">len(fragment)</span></code>.</p>

  277. </dd></dl>

  278. 

  279. <dl class="py function">

  280. <dt class="sig sig-object py" id="audioop.findfit">

  281. <span class="sig-prename descclassname"><span class="pre">audioop.</span></span><span class="sig-name descname"><span class="pre">findfit</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">fragment</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">reference</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#audioop.findfit" title="Link to this definition">¶</a></dt>

  282. <dd><p>Try to match <em>reference</em> as well as possible to a portion of <em>fragment</em> (which

  283. should be the longer fragment).  This is (conceptually) done by taking slices

  284. out of <em>fragment</em>, using <a class="reference internal" href="#audioop.findfactor" title="audioop.findfactor"><code class="xref py py-func docutils literal notranslate"><span class="pre">findfactor()</span></code></a> to compute the best match, and

  285. minimizing the result.  The fragments should both contain 2-byte samples.

  286. Return a tuple <code class="docutils literal notranslate"><span class="pre">(offset,</span> <span class="pre">factor)</span></code> where <em>offset</em> is the (integer) offset into

  287. <em>fragment</em> where the optimal match started and <em>factor</em> is the (floating-point)

  288. factor as per <a class="reference internal" href="#audioop.findfactor" title="audioop.findfactor"><code class="xref py py-func docutils literal notranslate"><span class="pre">findfactor()</span></code></a>.</p>

  289. </dd></dl>

  290. 

  291. <dl class="py function">

  292. <dt class="sig sig-object py" id="audioop.findmax">

  293. <span class="sig-prename descclassname"><span class="pre">audioop.</span></span><span class="sig-name descname"><span class="pre">findmax</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">fragment</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">length</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#audioop.findmax" title="Link to this definition">¶</a></dt>

  294. <dd><p>Search <em>fragment</em> for a slice of length <em>length</em> samples (not bytes!) with

  295. maximum energy, i.e., return <em>i</em> for which <code class="docutils literal notranslate"><span class="pre">rms(fragment[i*2:(i+length)*2])</span></code>

  296. is maximal.  The fragments should both contain 2-byte samples.</p>

  297. <p>The routine takes time proportional to <code class="docutils literal notranslate"><span class="pre">len(fragment)</span></code>.</p>

  298. </dd></dl>

  299. 

  300. <dl class="py function">

  301. <dt class="sig sig-object py" id="audioop.getsample">

  302. <span class="sig-prename descclassname"><span class="pre">audioop.</span></span><span class="sig-name descname"><span class="pre">getsample</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">fragment</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">width</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">index</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#audioop.getsample" title="Link to this definition">¶</a></dt>

  303. <dd><p>Return the value of sample <em>index</em> from the fragment.</p>

  304. </dd></dl>

  305. 

  306. <dl class="py function">

  307. <dt class="sig sig-object py" id="audioop.lin2adpcm">

  308. <span class="sig-prename descclassname"><span class="pre">audioop.</span></span><span class="sig-name descname"><span class="pre">lin2adpcm</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">fragment</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">width</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">state</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#audioop.lin2adpcm" title="Link to this definition">¶</a></dt>

  309. <dd><p>Convert samples to 4 bit Intel/DVI ADPCM encoding.  ADPCM coding is an adaptive

  310. coding scheme, whereby each 4 bit number is the difference between one sample

  311. and the next, divided by a (varying) step.  The Intel/DVI ADPCM algorithm has

  312. been selected for use by the IMA, so it may well become a standard.</p>

  313. <p><em>state</em> is a tuple containing the state of the coder.  The coder returns a tuple

  314. <code class="docutils literal notranslate"><span class="pre">(adpcmfrag,</span> <span class="pre">newstate)</span></code>, and the <em>newstate</em> should be passed to the next call

  315. of <a class="reference internal" href="#audioop.lin2adpcm" title="audioop.lin2adpcm"><code class="xref py py-func docutils literal notranslate"><span class="pre">lin2adpcm()</span></code></a>.  In the initial call, <code class="docutils literal notranslate"><span class="pre">None</span></code> can be passed as the state.

  316. <em>adpcmfrag</em> is the ADPCM coded fragment packed 2 4-bit values per byte.</p>

  317. </dd></dl>

  318. 

  319. <dl class="py function">

  320. <dt class="sig sig-object py" id="audioop.lin2alaw">

  321. <span class="sig-prename descclassname"><span class="pre">audioop.</span></span><span class="sig-name descname"><span class="pre">lin2alaw</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">fragment</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">width</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#audioop.lin2alaw" title="Link to this definition">¶</a></dt>

  322. <dd><p>Convert samples in the audio fragment to a-LAW encoding and return this as a

  323. bytes object.  a-LAW is an audio encoding format whereby you get a dynamic

  324. range of about 13 bits using only 8 bit samples.  It is used by the Sun audio

  325. hardware, among others.</p>

  326. </dd></dl>

  327. 

  328. <dl class="py function">

  329. <dt class="sig sig-object py" id="audioop.lin2lin">

  330. <span class="sig-prename descclassname"><span class="pre">audioop.</span></span><span class="sig-name descname"><span class="pre">lin2lin</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">fragment</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">width</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">newwidth</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#audioop.lin2lin" title="Link to this definition">¶</a></dt>

  331. <dd><p>Convert samples between 1-, 2-, 3- and 4-byte formats.</p>

  332. <div class="admonition note">

  333. <p class="admonition-title">Note</p>

  334. <p>In some audio formats, such as .WAV files, 16, 24 and 32 bit samples are

  335. signed, but 8 bit samples are unsigned.  So when converting to 8 bit wide

  336. samples for these formats, you need to also add 128 to the result:</p>

  337. <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="n">new_frames</span> <span class="o">=</span> <span class="n">audioop</span><span class="o">.</span><span class="n">lin2lin</span><span class="p">(</span><span class="n">frames</span><span class="p">,</span> <span class="n">old_width</span><span class="p">,</span> <span class="mi">1</span><span class="p">)</span>

  338. <span class="n">new_frames</span> <span class="o">=</span> <span class="n">audioop</span><span class="o">.</span><span class="n">bias</span><span class="p">(</span><span class="n">new_frames</span><span class="p">,</span> <span class="mi">1</span><span class="p">,</span> <span class="mi">128</span><span class="p">)</span>

  339. </pre></div>

  340. </div>

  341. <p>The same, in reverse, has to be applied when converting from 8 to 16, 24

  342. or 32 bit width samples.</p>

  343. </div>

  344. </dd></dl>

  345. 

  346. <dl class="py function">

  347. <dt class="sig sig-object py" id="audioop.lin2ulaw">

  348. <span class="sig-prename descclassname"><span class="pre">audioop.</span></span><span class="sig-name descname"><span class="pre">lin2ulaw</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">fragment</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">width</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#audioop.lin2ulaw" title="Link to this definition">¶</a></dt>

  349. <dd><p>Convert samples in the audio fragment to u-LAW encoding and return this as a

  350. bytes object.  u-LAW is an audio encoding format whereby you get a dynamic

  351. range of about 14 bits using only 8 bit samples.  It is used by the Sun audio

  352. hardware, among others.</p>

  353. </dd></dl>

  354. 

  355. <dl class="py function">

  356. <dt class="sig sig-object py" id="audioop.max">

  357. <span class="sig-prename descclassname"><span class="pre">audioop.</span></span><span class="sig-name descname"><span class="pre">max</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">fragment</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">width</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#audioop.max" title="Link to this definition">¶</a></dt>

  358. <dd><p>Return the maximum of the <em>absolute value</em> of all samples in a fragment.</p>

  359. </dd></dl>

  360. 

  361. <dl class="py function">

  362. <dt class="sig sig-object py" id="audioop.maxpp">

  363. <span class="sig-prename descclassname"><span class="pre">audioop.</span></span><span class="sig-name descname"><span class="pre">maxpp</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">fragment</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">width</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#audioop.maxpp" title="Link to this definition">¶</a></dt>

  364. <dd><p>Return the maximum peak-peak value in the sound fragment.</p>

  365. </dd></dl>

  366. 

  367. <dl class="py function">

  368. <dt class="sig sig-object py" id="audioop.minmax">

  369. <span class="sig-prename descclassname"><span class="pre">audioop.</span></span><span class="sig-name descname"><span class="pre">minmax</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">fragment</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">width</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#audioop.minmax" title="Link to this definition">¶</a></dt>

  370. <dd><p>Return a tuple consisting of the minimum and maximum values of all samples in

  371. the sound fragment.</p>

  372. </dd></dl>

  373. 

  374. <dl class="py function">

  375. <dt class="sig sig-object py" id="audioop.mul">

  376. <span class="sig-prename descclassname"><span class="pre">audioop.</span></span><span class="sig-name descname"><span class="pre">mul</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">fragment</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">width</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">factor</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#audioop.mul" title="Link to this definition">¶</a></dt>

  377. <dd><p>Return a fragment that has all samples in the original fragment multiplied by

  378. the floating-point value <em>factor</em>.  Samples are truncated in case of overflow.</p>

  379. </dd></dl>

  380. 

  381. <dl class="py function">

  382. <dt class="sig sig-object py" id="audioop.ratecv">

  383. <span class="sig-prename descclassname"><span class="pre">audioop.</span></span><span class="sig-name descname"><span class="pre">ratecv</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">fragment</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">width</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">nchannels</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">inrate</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">outrate</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">state</span></span></em><span class="optional">[</span>, <em class="sig-param"><span class="n"><span class="pre">weightA</span></span></em><span class="optional">[</span>, <em class="sig-param"><span class="n"><span class="pre">weightB</span></span></em><span class="optional">]</span><span class="optional">]</span><span class="sig-paren">)</span><a class="headerlink" href="#audioop.ratecv" title="Link to this definition">¶</a></dt>

  384. <dd><p>Convert the frame rate of the input fragment.</p>

  385. <p><em>state</em> is a tuple containing the state of the converter.  The converter returns

  386. a tuple <code class="docutils literal notranslate"><span class="pre">(newfragment,</span> <span class="pre">newstate)</span></code>, and <em>newstate</em> should be passed to the next

  387. call of <a class="reference internal" href="#audioop.ratecv" title="audioop.ratecv"><code class="xref py py-func docutils literal notranslate"><span class="pre">ratecv()</span></code></a>.  The initial call should pass <code class="docutils literal notranslate"><span class="pre">None</span></code> as the state.</p>

  388. <p>The <em>weightA</em> and <em>weightB</em> arguments are parameters for a simple digital filter

  389. and default to <code class="docutils literal notranslate"><span class="pre">1</span></code> and <code class="docutils literal notranslate"><span class="pre">0</span></code> respectively.</p>

  390. </dd></dl>

  391. 

  392. <dl class="py function">

  393. <dt class="sig sig-object py" id="audioop.reverse">

  394. <span class="sig-prename descclassname"><span class="pre">audioop.</span></span><span class="sig-name descname"><span class="pre">reverse</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">fragment</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">width</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#audioop.reverse" title="Link to this definition">¶</a></dt>

  395. <dd><p>Reverse the samples in a fragment and returns the modified fragment.</p>

  396. </dd></dl>

  397. 

  398. <dl class="py function">

  399. <dt class="sig sig-object py" id="audioop.rms">

  400. <span class="sig-prename descclassname"><span class="pre">audioop.</span></span><span class="sig-name descname"><span class="pre">rms</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">fragment</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">width</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#audioop.rms" title="Link to this definition">¶</a></dt>

  401. <dd><p>Return the root-mean-square of the fragment, i.e. <code class="docutils literal notranslate"><span class="pre">sqrt(sum(S_i^2)/n)</span></code>.</p>

  402. <p>This is a measure of the power in an audio signal.</p>

  403. </dd></dl>

  404. 

  405. <dl class="py function">

  406. <dt class="sig sig-object py" id="audioop.tomono">

  407. <span class="sig-prename descclassname"><span class="pre">audioop.</span></span><span class="sig-name descname"><span class="pre">tomono</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">fragment</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">width</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">lfactor</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">rfactor</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#audioop.tomono" title="Link to this definition">¶</a></dt>

  408. <dd><p>Convert a stereo fragment to a mono fragment.  The left channel is multiplied by

  409. <em>lfactor</em> and the right channel by <em>rfactor</em> before adding the two channels to

  410. give a mono signal.</p>

  411. </dd></dl>

  412. 

  413. <dl class="py function">

  414. <dt class="sig sig-object py" id="audioop.tostereo">

  415. <span class="sig-prename descclassname"><span class="pre">audioop.</span></span><span class="sig-name descname"><span class="pre">tostereo</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">fragment</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">width</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">lfactor</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">rfactor</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#audioop.tostereo" title="Link to this definition">¶</a></dt>

  416. <dd><p>Generate a stereo fragment from a mono fragment.  Each pair of samples in the

  417. stereo fragment are computed from the mono sample, whereby left channel samples

  418. are multiplied by <em>lfactor</em> and right channel samples by <em>rfactor</em>.</p>

  419. </dd></dl>

  420. 

  421. <dl class="py function">

  422. <dt class="sig sig-object py" id="audioop.ulaw2lin">

  423. <span class="sig-prename descclassname"><span class="pre">audioop.</span></span><span class="sig-name descname"><span class="pre">ulaw2lin</span></span><span class="sig-paren">(</span><em class="sig-param"><span class="n"><span class="pre">fragment</span></span></em>, <em class="sig-param"><span class="n"><span class="pre">width</span></span></em><span class="sig-paren">)</span><a class="headerlink" href="#audioop.ulaw2lin" title="Link to this definition">¶</a></dt>

  424. <dd><p>Convert sound fragments in u-LAW encoding to linearly encoded sound fragments.

  425. u-LAW encoding always uses 8 bits samples, so <em>width</em> refers only to the sample

  426. width of the output fragment here.</p>

  427. </dd></dl>

  428. 

  429. <p>Note that operations such as <a class="reference internal" href="#audioop.mul" title="audioop.mul"><code class="xref py py-func docutils literal notranslate"><span class="pre">mul()</span></code></a> or <a class="reference internal" href="#audioop.max" title="audioop.max"><code class="xref py py-func docutils literal notranslate"><span class="pre">max()</span></code></a> make no distinction

  430. between mono and stereo fragments, i.e. all samples are treated equal.  If this

  431. is a problem the stereo fragment should be split into two mono fragments first

  432. and recombined later.  Here is an example of how to do that:</p>

  433. <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">def</span> <span class="nf">mul_stereo</span><span class="p">(</span><span class="n">sample</span><span class="p">,</span> <span class="n">width</span><span class="p">,</span> <span class="n">lfactor</span><span class="p">,</span> <span class="n">rfactor</span><span class="p">):</span>

  434.     <span class="n">lsample</span> <span class="o">=</span> <span class="n">audioop</span><span class="o">.</span><span class="n">tomono</span><span class="p">(</span><span class="n">sample</span><span class="p">,</span> <span class="n">width</span><span class="p">,</span> <span class="mi">1</span><span class="p">,</span> <span class="mi">0</span><span class="p">)</span>

  435.     <span class="n">rsample</span> <span class="o">=</span> <span class="n">audioop</span><span class="o">.</span><span class="n">tomono</span><span class="p">(</span><span class="n">sample</span><span class="p">,</span> <span class="n">width</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="mi">1</span><span class="p">)</span>

  436.     <span class="n">lsample</span> <span class="o">=</span> <span class="n">audioop</span><span class="o">.</span><span class="n">mul</span><span class="p">(</span><span class="n">lsample</span><span class="p">,</span> <span class="n">width</span><span class="p">,</span> <span class="n">lfactor</span><span class="p">)</span>

  437.     <span class="n">rsample</span> <span class="o">=</span> <span class="n">audioop</span><span class="o">.</span><span class="n">mul</span><span class="p">(</span><span class="n">rsample</span><span class="p">,</span> <span class="n">width</span><span class="p">,</span> <span class="n">rfactor</span><span class="p">)</span>

  438.     <span class="n">lsample</span> <span class="o">=</span> <span class="n">audioop</span><span class="o">.</span><span class="n">tostereo</span><span class="p">(</span><span class="n">lsample</span><span class="p">,</span> <span class="n">width</span><span class="p">,</span> <span class="mi">1</span><span class="p">,</span> <span class="mi">0</span><span class="p">)</span>

  439.     <span class="n">rsample</span> <span class="o">=</span> <span class="n">audioop</span><span class="o">.</span><span class="n">tostereo</span><span class="p">(</span><span class="n">rsample</span><span class="p">,</span> <span class="n">width</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="mi">1</span><span class="p">)</span>

  440.     <span class="k">return</span> <span class="n">audioop</span><span class="o">.</span><span class="n">add</span><span class="p">(</span><span class="n">lsample</span><span class="p">,</span> <span class="n">rsample</span><span class="p">,</span> <span class="n">width</span><span class="p">)</span>

  441. </pre></div>

  442. </div>

  443. <p>If you use the ADPCM coder to build network packets and you want your protocol

  444. to be stateless (i.e. to be able to tolerate packet loss) you should not only

  445. transmit the data but also the state.  Note that you should send the <em>initial</em>

  446. state (the one you passed to <a class="reference internal" href="#audioop.lin2adpcm" title="audioop.lin2adpcm"><code class="xref py py-func docutils literal notranslate"><span class="pre">lin2adpcm()</span></code></a>) along to the decoder, not the

  447. final state (as returned by the coder).  If you want to use

  448. <a class="reference internal" href="struct.html#struct.Struct" title="struct.Struct"><code class="xref py py-class docutils literal notranslate"><span class="pre">struct.Struct</span></code></a> to store the state in binary you can code the first

  449. element (the predicted value) in 16 bits and the second (the delta index) in 8.</p>

  450. <p>The ADPCM coders have never been tried against other ADPCM coders, only against

  451. themselves.  It could well be that I misinterpreted the standards in which case

  452. they will not be interoperable with the respective standards.</p>

  453. <p>The <code class="xref py py-func docutils literal notranslate"><span class="pre">find*()</span></code> routines might look a bit funny at first sight. They are

  454. primarily meant to do echo cancellation.  A reasonably fast way to do this is to

  455. pick the most energetic piece of the output sample, locate that in the input

  456. sample and subtract the whole output sample from the input sample:</p>

  457. <div class="highlight-python3 notranslate"><div class="highlight"><pre><span></span><span class="k">def</span> <span class="nf">echocancel</span><span class="p">(</span><span class="n">outputdata</span><span class="p">,</span> <span class="n">inputdata</span><span class="p">):</span>

  458.     <span class="n">pos</span> <span class="o">=</span> <span class="n">audioop</span><span class="o">.</span><span class="n">findmax</span><span class="p">(</span><span class="n">outputdata</span><span class="p">,</span> <span class="mi">800</span><span class="p">)</span>    <span class="c1"># one tenth second</span>

  459.     <span class="n">out_test</span> <span class="o">=</span> <span class="n">outputdata</span><span class="p">[</span><span class="n">pos</span><span class="o">*</span><span class="mi">2</span><span class="p">:]</span>

  460.     <span class="n">in_test</span> <span class="o">=</span> <span class="n">inputdata</span><span class="p">[</span><span class="n">pos</span><span class="o">*</span><span class="mi">2</span><span class="p">:]</span>

  461.     <span class="n">ipos</span><span class="p">,</span> <span class="n">factor</span> <span class="o">=</span> <span class="n">audioop</span><span class="o">.</span><span class="n">findfit</span><span class="p">(</span><span class="n">in_test</span><span class="p">,</span> <span class="n">out_test</span><span class="p">)</span>

  462.     <span class="c1"># Optional (for better cancellation):</span>

  463.     <span class="c1"># factor = audioop.findfactor(in_test[ipos*2:ipos*2+len(out_test)],</span>

  464.     <span class="c1">#              out_test)</span>

  465.     <span class="n">prefill</span> <span class="o">=</span> <span class="s1">&#39;</span><span class="se">\0</span><span class="s1">&#39;</span><span class="o">*</span><span class="p">(</span><span class="n">pos</span><span class="o">+</span><span class="n">ipos</span><span class="p">)</span><span class="o">*</span><span class="mi">2</span>

  466.     <span class="n">postfill</span> <span class="o">=</span> <span class="s1">&#39;</span><span class="se">\0</span><span class="s1">&#39;</span><span class="o">*</span><span class="p">(</span><span class="nb">len</span><span class="p">(</span><span class="n">inputdata</span><span class="p">)</span><span class="o">-</span><span class="nb">len</span><span class="p">(</span><span class="n">prefill</span><span class="p">)</span><span class="o">-</span><span class="nb">len</span><span class="p">(</span><span class="n">outputdata</span><span class="p">))</span>

  467.     <span class="n">outputdata</span> <span class="o">=</span> <span class="n">prefill</span> <span class="o">+</span> <span class="n">audioop</span><span class="o">.</span><span class="n">mul</span><span class="p">(</span><span class="n">outputdata</span><span class="p">,</span> <span class="mi">2</span><span class="p">,</span> <span class="o">-</span><span class="n">factor</span><span class="p">)</span> <span class="o">+</span> <span class="n">postfill</span>

  468.     <span class="k">return</span> <span class="n">audioop</span><span class="o">.</span><span class="n">add</span><span class="p">(</span><span class="n">inputdata</span><span class="p">,</span> <span class="n">outputdata</span><span class="p">,</span> <span class="mi">2</span><span class="p">)</span>

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