diff --git a/shared-bindings/synthio/MidiTrack.c b/shared-bindings/synthio/MidiTrack.c
index 0304df12a81..6adb11e06c3 100644
--- a/shared-bindings/synthio/MidiTrack.c
+++ b/shared-bindings/synthio/MidiTrack.c
@@ -72,7 +72,7 @@ static mp_obj_t synthio_miditrack_make_new(const mp_obj_type_t *type, size_t n_a
     synthio_miditrack_obj_t *self = mp_obj_malloc(synthio_miditrack_obj_t, &synthio_miditrack_type);
     common_hal_synthio_miditrack_construct(self,
         (uint8_t *)bufinfo.buf, bufinfo.len,
-        args[ARG_tempo].u_int,
+        mp_arg_validate_int_min(args[ARG_tempo].u_int, 1, MP_QSTR_tempo),
         args[ARG_sample_rate].u_int,
         args[ARG_waveform].u_obj,
         mp_const_none,
diff --git a/shared-bindings/synthio/Synthesizer.c b/shared-bindings/synthio/Synthesizer.c
index 35cc42a2037..a5d053df302 100644
--- a/shared-bindings/synthio/Synthesizer.c
+++ b/shared-bindings/synthio/Synthesizer.c
@@ -63,7 +63,7 @@ static mp_obj_t synthio_synthesizer_make_new(const mp_obj_type_t *type, size_t n
 
     synthio_synthesizer_obj_t *self = mp_obj_malloc(synthio_synthesizer_obj_t, &synthio_synthesizer_type);
     common_hal_synthio_synthesizer_construct(self,
-        args[ARG_sample_rate].u_int,
+        mp_arg_validate_int_min(args[ARG_sample_rate].u_int, 1, MP_QSTR_sample_rate),
         args[ARG_channel_count].u_int,
         args[ARG_waveform].u_obj,
         args[ARG_envelope].u_obj);
diff --git a/shared-bindings/synthio/__init__.c b/shared-bindings/synthio/__init__.c
index 6a21834751b..5ef0b58b710 100644
--- a/shared-bindings/synthio/__init__.c
+++ b/shared-bindings/synthio/__init__.c
@@ -258,12 +258,6 @@ static mp_obj_t synthio_from_file(size_t n_args, const mp_obj_t *pos_args, mp_ma
         args[ARG_envelope].u_obj
         );
 
-    #if MICROPY_MALLOC_USES_ALLOCATED_SIZE
-    m_free(buffer, track_size);
-    #else
-    m_free(buffer);
-    #endif
-
     return MP_OBJ_FROM_PTR(result);
 }
 MP_DEFINE_CONST_FUN_OBJ_KW(synthio_from_file_obj, 1, synthio_from_file);
diff --git a/shared-module/synthio/MidiTrack.c b/shared-module/synthio/MidiTrack.c
index 1cccd440fad..7c54c36d47f 100644
--- a/shared-module/synthio/MidiTrack.c
+++ b/shared-module/synthio/MidiTrack.c
@@ -19,6 +19,7 @@ static mp_obj_t parse_note(synthio_miditrack_obj_t *self) {
     size_t len = self->track.len;
     if (self->pos + 1 >= len) {
         record_midi_stream_error(self);
+        return MP_OBJ_NEW_SMALL_INT(0);
     }
     uint8_t note = buffer[(self->pos)++];
     if (note > 127 || buffer[(self->pos)++] > 127) {
@@ -51,6 +52,9 @@ static void decode_until_pause(synthio_miditrack_obj_t *self) {
     uint8_t *buffer = self->track.buf;
     size_t len = self->track.len;
     do {
+        if (self->pos >= len) {
+            break;
+        }
         switch (buffer[self->pos++] >> 4) {
             case 8: { // Note Off
                 mp_obj_t note = parse_note(self);
diff --git a/shared-module/synthio/__init__.c b/shared-module/synthio/__init__.c
index 368bae24140..6201ad96347 100644
--- a/shared-module/synthio/__init__.c
+++ b/shared-module/synthio/__init__.c
@@ -224,14 +224,13 @@ static bool synth_note_into_buffer(synthio_synth_t *synth, int chan, int32_t *ou
     uint32_t lim = waveform_length << SYNTHIO_FREQUENCY_SHIFT;
     uint32_t accum = synth->accum[chan];
 
-    if (dds_rate > lim / 2) {
+    if (dds_rate > (lim - offset) / 2) {
         // beyond nyquist, can't play note
         return false;
     }
 
-    // can happen if note waveform gets set mid-note, but the expensive modulo is usually avoided
-    if (accum > lim) {
-        accum = accum % lim + offset;
+    if (accum >= lim) {
+        accum = accum < offset ? offset : offset + (accum - offset) % (lim - offset);
     }
 
     // first, fill with waveform
@@ -247,20 +246,19 @@ static bool synth_note_into_buffer(synthio_synth_t *synth, int chan, int32_t *ou
     synth->accum[chan] = accum;
 
     if (ring_dds_rate) {
-        if (ring_dds_rate > lim / 2) {
+        accum = synth->ring_accum[chan];
+        offset = ring_waveform_start << SYNTHIO_FREQUENCY_SHIFT;
+        lim = ring_waveform_length << SYNTHIO_FREQUENCY_SHIFT;
+
+        if (ring_dds_rate > (lim - offset) / 2) {
             // beyond nyquist, can't play ring (but did synth main sound so
             // return true)
             return true;
         }
 
-        // now modulate by ring and accumulate
-        accum = synth->ring_accum[chan];
-        offset = ring_waveform_start << SYNTHIO_FREQUENCY_SHIFT;
-        lim = ring_waveform_length << SYNTHIO_FREQUENCY_SHIFT;
-
         // can happen if note waveform gets set mid-note, but the expensive modulo is usually avoided
-        if (accum > lim) {
-            accum = accum % lim + offset;
+        if (accum >= lim) {
+            accum = accum < offset ? offset : offset + (accum - offset) % (lim - offset);
         }
 
         for (uint16_t i = 0; i < dur; i++) {
@@ -270,8 +268,8 @@ static bool synth_note_into_buffer(synthio_synth_t *synth, int chan, int32_t *ou
                 accum = accum - lim + offset;
             }
             int16_t idx = accum >> SYNTHIO_FREQUENCY_SHIFT;
-            int16_t wi = (ring_waveform[idx] * out_buffer32[i]) / 32768; // consider for synthio_sat16 but had a weird artificat
-            out_buffer32[i] = wi;
+            int32_t wi = (ring_waveform[idx] * out_buffer32[i]) / 32768;
+            out_buffer32[i] = wi > 32767 ? 32767 : wi;
         }
         synth->ring_accum[chan] = accum;
     }