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Clamp Gain, Scale input sample

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Add gain clamping +-dB
Scale input Sample
This commit is contained in:
Geoffrey Merck 2020-01-29 17:30:22 +01:00
parent 658a47bc4e
commit 53384f036c
2 changed files with 27 additions and 12 deletions
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31
ambed/cagc.cpp
View File

@ -36,17 +36,25 @@
CAGC::CAGC(float initialLeveldB)
{
// set internal gain appropriately
m_g = powf(10.0f, -initialLeveldB/20.0f);
m_g = pow(10.0f, initialLeveldB/20.0f);
// ensure resulting gain is not arbitrarily low
if (m_g < 1e-16f)
m_g = 1e-16f;
m_scale = 1.0f;
m_bandwidth = 1e-2f;
m_scale = (float)0xFFFF;
m_bandwidth = 1e-2f; //TODO : Move to parameter ?
m_gMax = pow(10.0f, initialLeveldB + 10.0f/20.0f);//+- 10dB Margin, TODO Move margin to constant
m_gMin = pow(10.0f, initialLeveldB - 10.0f/20.0f);
m_alpha = m_bandwidth;
m_y2_prime = 1.0f;
}
float CAGC::GetGain()
{
return 20.0f*log10(m_g);
}
void CAGC::Apply(uint8 * voice, int size)
{
for (int i = 0; i < size; i+=2)
@ -54,6 +62,11 @@ void CAGC::Apply(uint8 * voice, int size)
//Get the sample
float _x = (float)(short)MAKEWORD(voice[i+1], voice[i]);
//This AGC tries to smooth energy so it does not exceed 1
//Therefore divide by our max supposed value
//Maybe we could also change y2 prime calculation below, but for now stick with this
_x /= m_scale;
//apply AGC
// apply gain to input sample
float _y = _x * m_g;
@ -66,16 +79,18 @@ void CAGC::Apply(uint8 * voice, int size)
// update gain according to output energy
if (m_y2_prime > 1e-6f)
m_g *= exp( -0.5f * m_alpha * log(m_y2_prime) );
m_g *= exp( -0.5f * m_alpha * log(m_y2_prime) );
// clamp to 120 dB gain
if (m_g > 1e6f)
m_g = 1e6f;
// clamp gain
if (m_g > m_gMax)
m_g = m_gMax;
else if(m_g < m_gMin)
m_g = m_gMin;
// apply output scale
_y *= m_scale;
//write processed sample back to it
//write processed sample back
voice[i] = HIBYTE((short)_y);
voice[i+1] = LOBYTE((short)_y);
}

8
ambed/cagc.h
View File

@ -21,7 +21,7 @@
// You should have received a copy of the GNU General Public License
// along with Foobar. If not, see <http://www.gnu.org/licenses/>.
// ----------------------------------------------------------------------------
// Geoffrey Merck F4FXL / KC3FRA AGC code borrowed from Liquid DSP
// Geoffrey Merck F4FXL / KC3FRA AGC code largely inspired by Liquid DSP
// Only took the parts we need qnd recoeded it to be close the XLX coding style
// https://github.com/jgaeddert/liquid-dsp/blob/master/src/agc/src/agc.c
@ -29,7 +29,6 @@
#define cagc_h
#include "main.h"
#include "math.h"
class CAGC
{
@ -39,11 +38,12 @@ public:
//methods
void Apply(uint8 * voice, int size);
float GetGain(){ return -20.0f*log10(m_g); }//gets current gain
float GetGain();//gets current gain
private:
float m_g; // current gain value
float m_scale; // output scale value
float m_gMax, m_gMin; //gain clamping
float m_scale; // scale value
// gain control loop filter parameters
float m_bandwidth; // bandwidth-time constant