diff --git a/generate_test.py b/generate_test.py
index 141b11063c611a99668dd3346a5ca4fb693284db..6233b4211cb46bdf3e19974e883a9468765df2a8 100755
--- a/generate_test.py
+++ b/generate_test.py
@@ -42,8 +42,8 @@ EXPERIMENTS_P800 = [f"P800-{i}" for i in range(1, 10)]
 EXPERIMENTS_BS1534 = [f"BS1534-{i}{x}" for i in range(1, 8) for x in ["a", "b"]]
 LAB_IDS = ["a", "b", "c", "d"]
 IN_FMT_FOR_MASA_EXPS = {
-    "P800-8": dict(zip([f"cat{i}" for i in range(1, 7)], ["FOA"] * 6)),
-    "P800-9": dict(zip([f"cat{i}" for i in range(1, 7)], ["FOA"] * 6)),
+    "P800-8": {"cat1": "FOA", "cat2": "FOA", "cat3": "FOA", "cat4": "FOA", "cat5": "FOA", "cat6": "FOA"},
+    "P800-9": {"cat1": "FOA", "cat2": "FOA", "cat3": "FOA", "cat4": "FOA", "cat5": "FOA", "cat6": "FOA"},
     "BS1534-7a": {"cat1": "FOA", "cat2": "HOA2"},
     "BS1534-7b": {"cat1": "FOA", "cat2": "HOA2"},
 }
@@ -102,7 +102,7 @@ def create_experiment_setup(experiment, lab) -> list[Path]:
         input_path = base_path.joinpath("proc_input").joinpath(cat)
         output_path = base_path.joinpath("proc_output").joinpath(suffix)
         bg_noise_path = base_path.joinpath("background_noise").joinpath(
-            f"background_noise_{suffix}.wav"
+            f"background_noise_{cat}.wav"
         )
         cfg_path = default_cfg_path.parent.joinpath(f"{experiment}{cat}-lab_{lab}.yml")
         cfgs.append(cfg_path)
@@ -113,15 +113,18 @@ def create_experiment_setup(experiment, lab) -> list[Path]:
         cfg.prerun_seed = seed
         cfg.input_path = str(input_path)
         cfg.output_path = str(output_path)
+
+        cat_num = int(cat[-1])
         if (
             bg_noise_pre_proc_2 := cfg.preprocessing_2.get("background_noise", None)
         ) is not None:
             bg_noise_pre_proc_2["background_noise_path"] = str(bg_noise_path)
 
             # bg noise SNR only differs from default config for some experiments
-            cat_num = int(cat[-1])
             if experiment in ["P800-5", "P800-9"] and cat_num >= 3:
                 bg_noise_pre_proc_2["snr"] = 15
+        if cfg.preprocessing_2.get("concatenate_input", None) is not None:
+            cfg.preprocessing_2["concatenation_order"] = concatenation_order(lab, experiment, cat_num)
 
         # for MASA, the input format can differ between categories
         if (fmt_for_category := IN_FMT_FOR_MASA_EXPS.get(experiment, None)) is not None:
@@ -158,6 +161,11 @@ def exp_lab_pair(arg):
     return exp, lab
 
 
+def concatenation_order(lab_id, experiment, category):
+    exp_id = f"p0{experiment[-1]}"
+    return [f"{lab_id}{exp_id}a{category}s0{i}.wav" for i in range(1, 8)]
+
+
 if __name__ == "__main__":
     parser = argparse.ArgumentParser(
         description="Generate config files and process files for selecton experiments. Experiment names and lab ids must be given as comma-separated pairs (e.g. 'P800-5,b BS1534-4a,d ...')"
diff --git a/ivas_processing_scripts/processing/processing.py b/ivas_processing_scripts/processing/processing.py
index bcc8330fdeb0d2b120748ad612f65290a8eed404..8da8593ee3030e2eb00f6599c515cee672de10e2 100755
--- a/ivas_processing_scripts/processing/processing.py
+++ b/ivas_processing_scripts/processing/processing.py
@@ -83,6 +83,10 @@ def reorder_items_list(items_list: list, concatenation_order: list) -> list:
         Re-ordered list of input items
     """
     name_to_full = {Path(full_file).name: full_file for full_file in items_list}
+
+    if set(name_to_full.keys()) != set(concatenation_order):
+        raise ValueError(f"Items given in concatenation_order {concatenation_order} are not identical to what was found in the input folder {name_to_full.keys()}")
+
     ordered_full_files = [
         name_to_full[name] for name in concatenation_order if name in name_to_full
     ]
diff --git a/ivas_processing_scripts/utils.py b/ivas_processing_scripts/utils.py
index 1ad9319f7aa3b777cdd119f7ef50ac41cc82f6bd..6d29ba96f1a847b5c1934d5cfca87a07e209e014 100755
--- a/ivas_processing_scripts/utils.py
+++ b/ivas_processing_scripts/utils.py
@@ -127,6 +127,9 @@ def list_audio(path: str, select_list: list = None) -> list:
             f for f in audio_list if any([pattern in f.stem for pattern in select_set])
         ]
 
+    # sort file list alphanumerically by filenames
+    audio_list = sorted(audio_list, key=lambda p: p.name)
+
     return audio_list
 
 
diff --git a/tests/test_experiments.py b/tests/test_experiments.py
index b8e62114fde2b4867a56dfb7edcc11d6183a9c05..51d50e635c56683043b94f0d6c119eb28b5ca059 100644
--- a/tests/test_experiments.py
+++ b/tests/test_experiments.py
@@ -77,6 +77,7 @@ def setup_input_files_for_config(config):
     dummy_md_files = FORMAT_TO_METADATA_FILES.get(input_fmt, list())
 
     # copy input files
+    files_copied = list()
     for f in dummy_input_files:
         f_out = input_path.joinpath(f.name).resolve().absolute()
         # need at least 2s of input files for gen-patt to be happy (can not keep the tolerance for 50 frames only)
@@ -86,6 +87,8 @@ def setup_input_files_for_config(config):
             md_f_out = ".".join([str(f_out), suffix])
             shutil.copy(md_f, md_f_out)
 
+        files_copied.append(f_out.name)
+
     # create background noise files with white noise
     if "background_noise" in config.preprocessing_2:
         # always set the same seed to have reproducible test noises
@@ -98,6 +101,8 @@ def setup_input_files_for_config(config):
         ).absolute()
         write(bg_noise_path, noise)
 
+    return files_copied
+
 
 def all_lengths_equal(cfg):
     output_folder = cfg.output_path
@@ -132,7 +137,12 @@ def test_generate_test_items(exp_lab_pair):
     args = Arguments(str(cfg))
     config = TestConfig(cfg)
 
-    setup_input_files_for_config(config)
+    input_filenames = setup_input_files_for_config(config)
+    # patch concatenation order
+    if config.preprocessing_2.get("concatenate_input", None) is not None:
+        config.preprocessing_2["concatenation_order"] = sorted(input_filenames)
+        config.to_file(cfg)
+
     generate_test(args)
 
     if not all_lengths_equal(config):