Negative time constant for single pole lowpass filter means no time-weighting at all.

lasp/c/lasp_slm.c

@@ -20,10 +20,7 @@ Slm *Slm_create(Sosfilterbank *prefilter, Sosfilterbank *bandpass, const d fs,
   assertvalidptr(downsampling_fac);
 
   Slm *slm = NULL;
-    if (tau <= 0) {
+  if (ref_level <= 0) {
-        WARN("Invalid time constant");
-        return NULL;
-    } else if (ref_level <= 0) {
     WARN("Invalid reference level");
     return NULL;
   } else if (fs <= 0) {
@@ -41,10 +38,15 @@ Slm *Slm_create(Sosfilterbank *prefilter, Sosfilterbank *bandpass, const d fs,
   /// documentation for the computation of its minus 20 dB point. We set the
   /// reduction in its 'sampling frequency' such that its noise is at a level
   /// of 20 dB less than its 'signal'.
+  if (tau > 0) {
     const d fs_slm = 1 / (2 * number_pi * tau) * (1 - 0.01) / 0.01;
     slm->downsampling_fac = (us)(fs / fs_slm);
     slm->cur_offset = 0;
     *downsampling_fac = slm->downsampling_fac;
+  } else {
+    *downsampling_fac = 1;
+    slm->downsampling_fac = 1;
+  }
 
   /// Create the single pole lowpass
   us filterbank_size;
@@ -54,6 +56,8 @@ Slm *Slm_create(Sosfilterbank *prefilter, Sosfilterbank *bandpass, const d fs,
     filterbank_size = 1;
   }
 
+  if (tau > 0) {
+
     vd lowpass_sos = vd_alloc(6);
     d b0 = 1.0 / (1 + 2 * tau * fs);
     *getvdval(&lowpass_sos, 0) = b0;
@@ -70,6 +74,10 @@ Slm *Slm_create(Sosfilterbank *prefilter, Sosfilterbank *bandpass, const d fs,
       Sosfilterbank_setFilter(slm->splowpass[ch], 0, lowpass_sos);
     }
     vd_free(&lowpass_sos);
+  } else {
+    /// No low-pass filtering. Tau set to zero
+    slm->splowpass = NULL;
+  }
 
   feTRACE(15);
   return slm;
@@ -106,19 +114,26 @@ dmat Slm_run(Slm *slm, vd *input_data) {
   iVARTRACE(15, samples_bandpassed);
   us cur_offset = slm->cur_offset;
 
+  /// Compute the number of samples output
   int nsamples_output = (samples_bandpassed - cur_offset) / downsampling_fac;
   while (nsamples_output * downsampling_fac + cur_offset < samples_bandpassed)
     nsamples_output++;
-    if(nsamples_output < 0) nsamples_output = 0;
+  if (nsamples_output < 0)
+    nsamples_output = 0;
 
   iVARTRACE(15, nsamples_output);
   iVARTRACE(15, cur_offset);
 
-    dmat levels = dmat_alloc(nsamples_output, filterbank_size);
+  dmat levels;
+  if (slm->splowpass) {
+    levels = dmat_alloc(nsamples_output, filterbank_size);
+  } else {
+    levels = dmat_alloc(samples_bandpassed, filterbank_size);
+  }
 
   for (us ch = 0; ch < bandpassed.n_cols; ch++) {
     iVARTRACE(15, ch);
-        cur_offset = slm->cur_offset;
+    vd chan = dmat_column(&bandpassed, ch);
     /// Inplace squaring of the signal
     for (us sample = 0; sample < bandpassed.n_rows; sample++) {
       tmp = getdmatval(&bandpassed, sample, ch);
@@ -127,7 +142,8 @@ dmat Slm_run(Slm *slm, vd *input_data) {
 
     // Now that all data for the channel is squared, we can run it through
     // the low-pass filter
-        vd chan = dmat_column(&bandpassed, ch);
+    if (slm->splowpass) {
+      cur_offset = slm->cur_offset;
 
       /// Apply single-pole lowpass filter for current filterbank channel
       vd power_filtered = Sosfilterbank_filter(slm->splowpass[ch], &chan);
@@ -135,25 +151,32 @@ dmat Slm_run(Slm *slm, vd *input_data) {
 
       /// Output resulting levels at a lower interval
       us i = 0;
-        d level;
       while (cur_offset < samples_bandpassed) {
         iVARTRACE(10, i);
         iVARTRACE(10, cur_offset);
-            level = 10 * d_log10(*getvdval(&power_filtered, cur_offset) / ref_level /
+        /// Compute level
-                    ref_level);
+        d level = 10 * d_log10(*getvdval(&power_filtered, cur_offset) /
+                             ref_level / ref_level);
 
         *getdmatval(&levels, i++, ch) = level;
         cur_offset = cur_offset + downsampling_fac;
       }
       iVARTRACE(15, cur_offset);
       iVARTRACE(15, i);
-        dbgassert(i == nsamples_output, "BUG");
+      dbgassert(i == (int) nsamples_output, "BUG");
 
       vd_free(&chan);
       vd_free(&power_filtered);
     }
+  }
   slm->cur_offset = cur_offset - samples_bandpassed;
 
+  if (!slm->splowpass) {
+    /// Raw copy of to levels. Happens only when the low-pass filter does not
+    /// have to come into action.
+    dmat_copy(&levels, &bandpassed);
+  }
+
   vd_free(&prefiltered);
   dmat_free(&bandpassed);
   feTRACE(15);
@@ -166,7 +189,6 @@ void Slm_free(Slm *slm) {
   if (slm->prefilter) {
     Sosfilterbank_free(slm->prefilter);
   }
-    assertvalidptr(slm->splowpass);
 
   us filterbank_size;
   if (slm->bandpass) {
@@ -175,11 +197,12 @@ void Slm_free(Slm *slm) {
   } else {
     filterbank_size = 1;
   }
+  if (slm->splowpass) {
     for (us ch = 0; ch < filterbank_size; ch++) {
       Sosfilterbank_free(slm->splowpass[ch]);
     }
     a_free(slm->splowpass);
-
+  }
   a_free(slm);
 
   feTRACE(15);