diff --git a/cw/tvla.py b/cw/tvla.py
index 89dc4935..61de609d 100755
--- a/cw/tvla.py
+++ b/cw/tvla.py
@@ -488,6 +488,27 @@ def run_tvla(ctx: typer.Context):
         # Amount of tolerable deviation from average during filtering.
         num_sigmas = 3.5
 
+        # Slice of wave file
+        # these options are only tested for otbn
+        if ("sample_start" in cfg and cfg["sample_start"] is not None):
+            sample_start = cfg["sample_start"]
+        else:
+            sample_start = 0
+
+        assert sample_start < len(project.waves[0])
+
+        if ("num_samples" in cfg and cfg["num_samples"] is not None):
+            num_samples = cfg["num_samples"]
+        else:
+            num_samples = len(project.waves[0]) - sample_start
+
+        if (num_samples + sample_start > len(project.waves[0])):
+            log.warning(f"Selected sample window {sample_start} to " +
+                        f"{sample_start+num_samples} is out of range!")
+            num_samples = len(project.waves[0]) - sample_start
+            log.warning(f"Will use samples from {sample_start} " +
+                        f"to {sample_start+num_samples} instead!")
+
         # Overall number of traces, trace start and end indices.
         num_traces_max = len(project.waves)
         if cfg["trace_start"] is None:
@@ -548,8 +569,11 @@ def run_tvla(ctx: typer.Context):
                 log.info("Converting Traces")
                 if project.waves[0].dtype == 'uint16':
                     traces = np.empty((num_traces, num_samples), dtype=np.uint16)
+                    log.info(f"Will use samples from {sample_start} to {sample_start+num_samples}")
                     for i_trace in range(num_traces):
-                        traces[i_trace] = project.waves[i_trace + trace_start]
+                        traces[i_trace] = project.waves[i_trace +
+                                                        trace_start][sample_start:sample_start +
+                                                                     num_samples]
                 else:
                     traces = np.empty((num_traces, num_samples), dtype=np.double)
                     for i_trace in range(num_traces):
diff --git a/cw/tvla_cfg_otbn.yaml b/cw/tvla_cfg_otbn.yaml
index ea1bb3d7..3ed2cd19 100644
--- a/cw/tvla_cfg_otbn.yaml
+++ b/cw/tvla_cfg_otbn.yaml
@@ -14,3 +14,5 @@ plot_figures: true
 general_test: true
 mode: otbn
 key_len_bytes: 40
+sample_start: null
+num_samples : 4000
diff --git a/cw/tvla_cfg_template.yaml b/cw/tvla_cfg_template.yaml
index 84aacf08..5e9df908 100644
--- a/cw/tvla_cfg_template.yaml
+++ b/cw/tvla_cfg_template.yaml
@@ -13,3 +13,6 @@ ttest_step_file: null
 plot_figures: false
 general_test: true
 mode: aes
+# Only enabled for otbn mode.
+sample_start: null 
+num_samples : null