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<div class="refentry" title="dnoise">
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<h2>
<span class="refentrytitle">dnoise</span>
</h2>
<p>dnoise —
Reduces noise in a file.
<a id="IndexDnoise" class="indexterm"></a>
</p>
</div>
<div class="refsect1" title="Description">
<a id="idp81554104"></a>
<h2>Description</h2>
<p>
This is a noise reduction scheme using frequency-domain noise-gating.
</p>
</div>
<div class="refsect1" title="Syntax">
<a id="idp81554784"></a>
<h2>Syntax</h2>
<pre class="synopsis"><span class="command"><strong>dnoise</strong></span> [flags] -i noise_ref_file -o output_soundfile input_soundfile</pre>
</div>
<div class="refsect1" title="Initialization">
<a id="idp81589864"></a>
<h2>Initialization</h2>
<p>
Dnoise specific flags:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" type="disc">
<li class="listitem">
<p><span class="emphasis"><em>(no flag)</em></span> input soundfile to be denoised</p>
</li>
<li class="listitem">
<p><span class="emphasis"><em>-i fname</em></span> input reference noise soundfile</p>
</li>
<li class="listitem">
<p><span class="emphasis"><em>-o fname</em></span> output soundfile</p>
</li>
<li class="listitem">
<p><span class="emphasis"><em>-N fnum</em></span> # of bandpass filters (default: 1024)</p>
</li>
<li class="listitem">
<p><span class="emphasis"><em>-w fovlp</em></span> filter overlap factor: {0,1,(2),3} DON'T USE <span class="emphasis"><em>-w</em></span> AND <span class="emphasis"><em>-M</em></span></p>
</li>
<li class="listitem">
<p><span class="emphasis"><em>-M awlen</em></span> analysis window length (default: N-1 unless <span class="emphasis"><em>-w</em></span> is specified)</p>
</li>
<li class="listitem">
<p><span class="emphasis"><em>-L swlen</em></span> synthesis window length (default: M)</p>
</li>
<li class="listitem">
<p><span class="emphasis"><em>-D dfac</em></span> decimation factor (default: M/8)</p>
</li>
<li class="listitem">
<p><span class="emphasis"><em>-b btim</em></span> begin time in noise reference soundfile (default: 0)</p>
</li>
<li class="listitem">
<p><span class="emphasis"><em>-B smpst</em></span> starting sample in noise reference soundfile (default: 0)</p>
</li>
<li class="listitem">
<p><span class="emphasis"><em>-e etim</em></span> end time in noise reference soundfile (default: end of file)</p>
</li>
<li class="listitem">
<p><span class="emphasis"><em>-E smpend</em></span> final sample in noise reference soundfile (default: end of file)</p>
</li>
<li class="listitem">
<p><span class="emphasis"><em>-t thr</em></span> threshold above noise reference in dB (default: 30)</p>
</li>
<li class="listitem">
<p><span class="emphasis"><em>-S gfact</em></span> sharpness of noise-gate turnoff, range: 1 to 5 (default: 1)</p>
</li>
<li class="listitem">
<p><span class="emphasis"><em>-n numfrm</em></span> number of FFT frames to average over (default: 5)</p>
</li>
<li class="listitem">
<p><span class="emphasis"><em>-m mingain</em></span> minimum gain of noise-gate when off in dB (default: -40)</p>
</li>
</ul>
</div>
<p>
</p>
<p>
Soundfile format options:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" type="disc">
<li class="listitem">
<p><span class="emphasis"><em>-A</em></span> AIFF format output</p>
</li>
<li class="listitem">
<p><span class="emphasis"><em>-W</em></span> WAV format output</p>
</li>
<li class="listitem">
<p><span class="emphasis"><em>-J</em></span> IRCAM format output</p>
</li>
<li class="listitem">
<p><span class="emphasis"><em>-h</em></span> skip soundfile header (not valid for AIFF/WAV output)</p>
</li>
<li class="listitem">
<p><span class="emphasis"><em>-8</em></span> 8-bit unsigned char sound samples</p>
</li>
<li class="listitem">
<p><span class="emphasis"><em>-c</em></span> 8-bit signed_char sound samples</p>
</li>
<li class="listitem">
<p><span class="emphasis"><em>-a</em></span> alaw sound samples</p>
</li>
<li class="listitem">
<p><span class="emphasis"><em>-u</em></span> ulaw sound samples</p>
</li>
<li class="listitem">
<p><span class="emphasis"><em>-s</em></span> short_int sound samples</p>
</li>
<li class="listitem">
<p><span class="emphasis"><em>-l</em></span> long_int sound samples</p>
</li>
<li class="listitem">
<p><span class="emphasis"><em>-f</em></span> float sound samples. Floats also supported for WAV files. (New in Csound 3.47.)</p>
</li>
</ul>
</div>
<p>
</p>
<p>
Additional options:
</p>
<div class="itemizedlist">
<ul class="itemizedlist" type="disc">
<li class="listitem">
<p><span class="emphasis"><em>-R</em></span> verbose - print status info</p>
</li>
<li class="listitem">
<p><span class="emphasis"><em>-H [N]</em></span> print a heartbeat character at each soundfile write.</p>
</li>
<li class="listitem">
<p><span class="emphasis"><em>-- fname</em></span> output to log file fname</p>
</li>
<li class="listitem">
<p><span class="emphasis"><em>-V</em></span> verbose - print status info</p>
</li>
</ul>
</div>
<p>
</p>
<div class="note" title="Note" style="margin-left: 0.5in; margin-right: 0.5in;">
<table border="0" summary="Note: Note">
<tr>
<td rowspan="2" align="center" valign="top" width="25">
<img alt="[Note]" src="images/note.png" />
</td>
<th align="left">Note</th>
</tr>
<tr>
<td align="left" valign="top">
<p>
DNOISE also looks at the environment variable SFOUTYP to determine soundfile output format.
</p>
<p>
The -i flag is used for a reference noise file (normally created from a short section of the denoised file, where only noise is audible). The input soundfile to be denoised can be given anywhere on the command line, without a flag.
</p>
</td>
</tr>
</table>
</div>
</div>
<div class="refsect1" title="Performance">
<a id="idp81606960"></a>
<h2>Performance</h2>
<p>
This is a noise reduction scheme using frequency-domain noise-gating. This should work best in the case of high signal-to-noise with hiss-type noise.
</p>
<p>
The algorithm is that suggested by Moorer & Berger in <span class="quote">“<span class="quote">Linear-Phase Bandsplitting: Theory and Applications</span>”</span> presented at the 76th Convention 1984 October 8-11 New York of the Audio Engineering Society (preprint #2132) except that it uses the Weighted Overlap-Add formulation for short-time Fourier analysis-synthesis in place of the recursive formulation suggested by Moorer & Berger. The gain in each frequency bin is computed independently according to
</p>
<div class="literallayout">
<p><br />
gain = g0 + (1-g0) * [avg / (avg + th*th*nref)] ^ sh<br />
</p>
</div>
<p>
where <span class="emphasis"><em>avg</em></span> and <span class="emphasis"><em>nref</em></span> are the mean squared signal and noise respectively for the bin in question. (This is slightly different than in Moorer & Berger.)
</p>
<p>
The critical parameters <span class="emphasis"><em>th</em></span> and <span class="emphasis"><em>g0</em></span> are specified in dB and internally converted to decimal values. The <span class="emphasis"><em>nref</em></span> values are computed at the start of the program on the basis of a noise_soundfile (specified in the command line) which contains noise without signal.
</p>
<p>
The <span class="emphasis"><em>avg</em></span> values are computed over a rectangular window of m FFT frames looking both ahead and behind the current time. This corresponds to a temporal extent of m*D/R (which is typically (m*N/8)/R). The default settings of N, M, and D should be appropriate for most uses. A higher sample rate than 16 Khz might indicate a higher N.
</p>
</div>
<div class="refsect1" title="Credits">
<a id="idp81612008"></a>
<h2>Credits</h2>
<p>Author: Mark Dolson</p>
<p>August 26, 1989</p>
<p>Author: John ffitch</p>
<p>December 30, 2000</p>
<p>Updated by Rasmus Ekman on March 11, 2002.</p>
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