From 33058f2b292b3a581333bdfb21b8f671898c5060 Mon Sep 17 00:00:00 2001 From: Peter Bengtsson Date: Tue, 8 Dec 2020 14:40:17 -0500 Subject: initial commit --- .../api/audiocontext/createperiodicwave/index.html | 139 +++++++++++++++++++++ 1 file changed, 139 insertions(+) create mode 100644 files/ja/web/api/audiocontext/createperiodicwave/index.html (limited to 'files/ja/web/api/audiocontext/createperiodicwave/index.html') diff --git a/files/ja/web/api/audiocontext/createperiodicwave/index.html b/files/ja/web/api/audiocontext/createperiodicwave/index.html new file mode 100644 index 0000000000..825a1a8de5 --- /dev/null +++ b/files/ja/web/api/audiocontext/createperiodicwave/index.html @@ -0,0 +1,139 @@ +--- +title: AudioContext.createPeriodicWave() +slug: Web/API/AudioContext/createPeriodicWave +translation_of: Web/API/BaseAudioContext/createPeriodicWave +--- +

{{ APIRef("Web Audio API") }}

+ +
+

{{ domxref("AudioContext") }}インターフェースのcreatePeriodicWave()メソッドは、周期的な波形を定義するために使われる{{domxref("PeriodicWave")}}を生成します。これは{{ domxref("OscillatorNode") }}の出力を決めるために使われます。

+
+ +

構文

+ +
var audioCtx = new AudioContext();
+var wave = audioCtx.createPeriodicWave(real, imag);
+ +

戻り値

+ +

{{domxref("PeriodicWave")}}

+ +

引数

+ +
+
real
+
余弦項の配列 (伝統的なA項)
+
imag
+
正弦項の配列 (伝統的なB項)
+
+ +

例

+ +

The following example illustrates simple usage of createPeriodicWave(), to create a {{domxref("PeriodicWave")}} object containing a simple sine wave.

+ +
var real = new Float32Array(2);
+var imag = new Float32Array(2);
+var ac = new AudioContext();
+var osc = ac.createOscillator();
+
+real[0] = 0;
+imag[0] = 0;
+real[1] = 1;
+imag[1] = 0;
+
+var wave = ac.createPeriodicWave(real, imag);
+
+osc.setPeriodicWave(wave);
+
+osc.connect(ac.destination);
+
+osc.start();
+osc.stop(2);
+ +

This works because a sound that contains only a fundamental tone is by definition a sine wave.
+
+ Here, we create a PeriodicWave with two values. The first value is the DC offset, which is the value at which the oscillator starts. 0 is good here, because we want to start the curve at the middle of the [-1.0; 1.0] range.

+ +

The second and subsequent values are sine and cosine components. You can think of it as the result of a Fourier transform, where you get frequency domain values from time domain value. Here, with createPeriodicWave(), you specify the frequencies, and the browser performs a an inverse Fourier transform to get a time domain buffer for the frequency of the oscillator. Here, we only set one component at full volume (1.0) on the fundamental tone, so we get a sine wave.

+ +

The coefficients of the Fourier transform should be given in ascending order (i.e. (a+bi)ei,(c+di)e2i,(f+gi)e3i\left(a+bi\right)e^{i} , \left(c+di\right)e^{2i} , \left(f+gi\right)e^{3i}   etc.) and can be positive or negative.  A simple way of manually obtaining such coefficients (though not the best) is to use a graphing calculator.

+ +

仕様

+ + + + + + + + + + + + + + +
SpecificationStatusComment
{{SpecName('Web Audio API', '#widl-AudioContext-createPeriodicWave-PeriodicWave-Float32Array-real-Float32Array-imag', 'createPeriodicWave')}}{{Spec2('Web Audio API')}} 
+ +

ブラウザ互換性

+ +
{{CompatibilityTable}}
+ +
+ + + + + + + + + + + + + + + + + + + +
FeatureChromeFirefox (Gecko)Internet ExplorerOperaSafari (WebKit)
Basic support{{CompatChrome(10.0)}}{{property_prefix("webkit")}}{{CompatGeckoDesktop(25.0)}} {{CompatNo}}15.0{{property_prefix("webkit")}}
+ 22 (unprefixed)		6.0{{property_prefix("webkit")}}
+
+ +
+ + + + + + + + + + + + + + + + + + + + + + + + + +
FeatureAndroidAndroid WebviewFirefox Mobile (Gecko)Firefox OSIE MobileOpera MobileSafari MobileChrome for Android
Basic support{{CompatUnknown}}{{CompatVersionUnknown}}26.01.2{{CompatUnknown}}{{CompatUnknown}}{{CompatUnknown}}{{CompatChrome(33.0)}}
+
+ +

参考

+ + -- cgit v1.2.3-54-g00ecf