Add simple AudioAmplifier

gui/index.html

 		{"type":"AudioOutputTDM","data":{"defaults":{"name":{"value":"new"}},"shortName":"tdm","inputs":16,"outputs":0,"category":"output-function","color":"#E6E0F8","icon":"arrow-in.png"}},
 		{"type":"AudioOutputADAT","data":{"defaults":{"name":{"value":"new"}},"shortName":"adat","inputs":8,"outputs":0,"category":"output-function","color":"#E6E0F8","icon":"arrow-in.png"}},
 		{"type":"AudioOutputUSB","data":{"defaults":{"name":{"value":"new"}},"shortName":"usb","inputs":2,"outputs":0,"category":"output-function","color":"#E6E0F8","icon":"arrow-in.png"}},
+		{"type":"AudioAmplifier","data":{"defaults":{"name":{"value":"new"}},"shortName":"amp","inputs":1,"outputs":1,"category":"mixer-function","color":"#E6E0F8","icon":"arrow-in.png"}},
 		{"type":"AudioMixer4","data":{"defaults":{"name":{"value":"new"}},"shortName":"mixer","inputs":4,"outputs":1,"category":"mixer-function","color":"#E6E0F8","icon":"arrow-in.png"}},
 		{"type":"AudioPlayMemory","data":{"defaults":{"name":{"value":"new"}},"shortName":"playMem","inputs":0,"outputs":1,"category":"play-function","color":"#E6E0F8","icon":"arrow-in.png"}},
 		{"type":"AudioPlaySdWav","data":{"defaults":{"name":{"value":"new"}},"shortName":"playSdWav","inputs":0,"outputs":2,"category":"play-function","color":"#E6E0F8","icon":"arrow-in.png"}},
 	</div>
 </script>
 
+<script type="text/x-red" data-help-name="AudioAmplifier">
+	<h3>Summary</h3>
+	<div class=tooltipinfo>
+	<p>Amplify or attenuate a signal, or switch it on/off.
+		</p>
+	</div>
+	<h3>Audio Connections</h3>
+	<table class=doc align=center cellpadding=3>
+		<tr class=top><th>Port</th><th>Purpose</th></tr>
+		<tr class=odd><td align=center>In 0</td><td>Input signal</td></tr>
+		<tr class=odd><td align=center>Out 0</td><td>Amplified/Attn. Output</td></tr>
+	</table>
+	<h3>Functions</h3>
+	<p class=func><span class=keyword>gain</span>(level);</p>
+	<p class=desc>Adjust the amplification or attenuation.
+		"level" may be any floating point number from 0 to 32767.0.
+		1.0 passes the signal through directly.  Level of 0 shuts the channel
+		off completely.  Between 0 to 1.0 attenuates the signal, and above
+		1.0 amplifies it.  Negative numbers may also be used, to invert the
+		signal.
+	</p>
+	<!--<h3>Examples</h3>
+	<p class=exam>File &gt; Examples &gt; Audio &gt; SamplePlayer
+	</p>-->
+	<h3>Notes</h3>
+	<p>Gain of 0 and 1.0 are handled efficiently as special cases.  Zero
+		discards data without processing.  1.0 passes data directly, with
+		minimal overhead</p>
+	<p>Signal clipping can occur when any channel has gain greater than 1.0</p>
+</script>
+<script type="text/x-red" data-template-name="AudioAmplifier">
+	<div class="form-row">
+		<label for="node-input-name"><i class="fa fa-tag"></i> Name</label>
+		<input type="text" id="node-input-name" placeholder="Name">
+	</div>
+</script>
+
 <script type="text/x-red" data-help-name="AudioMixer4">
 	<h3>Summary</h3>
 	<div class=tooltipinfo>

keywords.txt

 AudioInputAnalog	KEYWORD2
 AudioInputAnalogStereo	KEYWORD2
 AudioMixer4	KEYWORD2
+AudioAmplifier	KEYWORD2
 AudioOutputAnalog	KEYWORD2
 AudioOutputAnalogStereo	KEYWORD2
 AudioPlayMemory	KEYWORD2

mixer.cpp

 	}
 }
 
-
+void AudioAmplifier::update(void)
+{
+	audio_block_t *block;
+	int32_t mult = multiplier;
+
+	if (mult == 0) {
+		// zero gain, discard any input and transmit nothing
+		block = receiveReadOnly(0);
+		if (block) release(block);
+	} else if (mult == MULTI_UNITYGAIN) {
+		// unity gain, pass input to output without any change
+		block = receiveReadOnly(0);
+		if (block) {
+			transmit(block);
+			release(block);
+		}
+	} else {
+		// apply gain to signal
+		block = receiveWritable(0);
+		if (block) {
+			applyGain(block->data, mult);
+			transmit(block);
+			release(block);
+		}
+	}
+}

mixer.h

 {
 #if defined(KINETISK)
 public:
-        AudioMixer4(void) : AudioStream(4, inputQueueArray) {
+	AudioMixer4(void) : AudioStream(4, inputQueueArray) {
 		for (int i=0; i<4; i++) multiplier[i] = 65536;
 	}
-        virtual void update(void);
+	virtual void update(void);
 	void gain(unsigned int channel, float gain) {
 		if (channel >= 4) return;
 		if (gain > 32767.0f) gain = 32767.0f;
 
 #elif defined(KINETISL)
 public:
-        AudioMixer4(void) : AudioStream(4, inputQueueArray) {
+	AudioMixer4(void) : AudioStream(4, inputQueueArray) {
 		for (int i=0; i<4; i++) multiplier[i] = 256;
 	}
-        virtual void update(void);
+	virtual void update(void);
 	void gain(unsigned int channel, float gain) {
 		if (channel >= 4) return;
 		if (gain > 127.0f) gain = 127.0f;
 #endif
 };
 
+class AudioAmplifier : public AudioStream
+{
+public:
+	AudioAmplifier(void) : AudioStream(1, inputQueueArray), multiplier(65536) {
+	}
+	virtual void update(void);
+	void gain(float n) {
+		if (n > 32767.0f) n = 32767.0f;
+		else if (n < -32767.0f) n = -32767.0f;
+		multiplier = n * 65536.0f;
+	}
+private:
+	int32_t multiplier;
+	audio_block_t *inputQueueArray[1];
+};
+
 #endif