1 page.title=Floating-Point Audio 2 @jd:body 3 4 <div id="qv-wrapper"> 5 <div id="qv"> 6 <h2>On this page</h2> 7 8 <ol> 9 <li><a href="#best">Best Practices for Floating-Point Audio</a></li> 10 <li><a href="#support">Floating-Point Audio in Android SDK</a></li> 11 <li><a href="#more">For More Information</a></li> 12 </ol> 13 </div> 14 </div> 15 16 <a href="https://www.youtube.com/watch?v=sIcieUqMml8" class="notice-developers-video"> 17 <div> 18 <h3>Video</h3> 19 <p>Will it Float? The Glory and Shame of Floating-Point Audio</p> 20 </div> 21 </a> 22 23 <p>Using floating-point numbers to represent audio data can significantly enhance audio 24 quality in high-performance audio applications. Floating point offers the following 25 advantages:</p> 26 27 <ul> 28 <li>Wider dynamic range.</li> 29 <li>Consistent accuracy across the dynamic range.</li> 30 <li>More headroom to avoid clipping during intermediate calculations and transients.</li> 31 </ul> 32 33 <p>While floating-point can enhance audio quality, it does present certain disadvantages:</p> 34 35 <ul> 36 <li>Floating-point numbers use more memory.</li> 37 <li>Floating-point operations employ unexpected properties, for example, addition is 38 not associative.</li> 39 <li>Floating-point calculations can sometimes lose arithmetic precision due to rounding or 40 numerically unstable algorithms.</li> 41 <li>Using floating-point effectively requires greater understanding to achieve accurate 42 and reproducible results.</li> 43 </ul> 44 45 <p> 46 Formerly, floating-point was notorious for being unavailable or slow. This is 47 still true for low-end and embedded processors. But processors on modern 48 mobile devices now have hardware floating-point with performance that is 49 similar (or in some cases even faster) than integer. Modern CPUs also support 50 <a href="http://en.wikipedia.org/wiki/SIMD" class="external-link">SIMD</a> 51 (Single instruction, multiple data), which can improve performance further. 52 </p> 53 54 <h2 id="best">Best Practices for Floating-Point Audio</h2> 55 <p>The following best practices help you avoid problems with floating-point calculations:</p> 56 <ul> 57 <li>Use double precision floating-point for infrequent calculations, 58 such as computing filter coefficients.</li> 59 <li>Pay attention to the order of operations.</li> 60 <li>Declare explicit variables for intermediate values.</li> 61 <li>Use parentheses liberally.</li> 62 <li>If you get a NaN or infinity result, use binary search to discover 63 where it was introduced.</li> 64 </ul> 65 66 <h2 id="support">Floating-Point Audio in Android SDK</h2> 67 68 <p>For floating-point audio, the audio format encoding 69 <code>AudioFormat.ENCODING_PCM_FLOAT</code> is used similarly to 70 <code>ENCODING_PCM_16_BIT</code> or <code>ENCODING_PCM_8_BIT</code> for specifying 71 AudioTrack data 72 formats. The corresponding overloaded method <code>AudioTrack.write()</code> 73 takes in a float array to deliver data.</p> 74 75 <pre> 76 public int write(float[] audioData, 77 int offsetInFloats, 78 int sizeInFloats, 79 int writeMode) 80 </pre> 81 82 <h2 id="more">For More Information</h2> 83 84 <p>The following Wikipedia pages are helpful in understanding floating-point audio:</p> 85 86 <ul> 87 <li><a href="http://en.wikipedia.org/wiki/Audio_bit_depth" class="external-link" >Audio bit depth</a></li> 88 <li><a href="http://en.wikipedia.org/wiki/Floating_point" class="external-link" >Floating point</a></li> 89 <li><a href="http://en.wikipedia.org/wiki/IEEE_floating_point" class="external-link" >IEEE 754 floating-point</a></li> 90 <li><a href="http://en.wikipedia.org/wiki/Loss_of_significance" class="external-link" >Loss of significance</a> 91 (catastrophic cancellation)</li> 92 <li><a href="https://en.wikipedia.org/wiki/Numerical_stability" class="external-link" >Numerical stability</a></li> 93 </ul> 94 95 <p>The following article provides information on those aspects of floating-point that have a 96 direct impact on designers of computer systems:</p> 97 <ul> 98 <li><a href="http://docs.oracle.com/cd/E19957-01/806-3568/ncg_goldberg.html" class="external-link" >What every 99 computer scientist should know about floating-point arithmetic</a> 100 by David Goldberg, Xerox PARC (edited reprint).</li> 101 </ul> 102
