diff --git a/module_usb_audio/usb_buffer/decouple.xc b/module_usb_audio/usb_buffer/decouple.xc
index 4cac7acc..806be67b 100644
--- a/module_usb_audio/usb_buffer/decouple.xc
+++ b/module_usb_audio/usb_buffer/decouple.xc
@@ -14,18 +14,18 @@
 #endif
 #define MAX(x,y) ((x)>(y) ? (x) : (y))
 
-#define CLASS_TWO_PACKET_SIZE ((((MAX_FREQ+7999)/8000))+3)     // Samples per channel
-#define CLASS_ONE_PACKET_SIZE  ((((MAX_FREQ_FS+999)/1000))+3)  // Samples per channel
+#define HS_PACKET_SIZE ((((MAX_FREQ+7999)/8000))+3)     // Samples per channel
+#define FS_PACKET_SIZE  ((((MAX_FREQ_FS+999)/1000))+3)  // Samples per channel
 
-/* TODO user SLOTSIZE to potentially save memory */
-#define BUFF_SIZE_OUT MAX(4 * CLASS_TWO_PACKET_SIZE * NUM_USB_CHAN_OUT, 4 * CLASS_ONE_PACKET_SIZE * NUM_USB_CHAN_OUT_FS)
-#define BUFF_SIZE_IN  MAX(4 * CLASS_TWO_PACKET_SIZE * NUM_USB_CHAN_IN, 4 * CLASS_ONE_PACKET_SIZE * NUM_USB_CHAN_IN_FS)
+/* TODO use SLOTSIZE to potentially save memory */
+#define BUFF_SIZE_OUT MAX(4 * HS_PACKET_SIZE * NUM_USB_CHAN_OUT, 4 * FS_PACKET_SIZE * NUM_USB_CHAN_OUT_FS)
+#define BUFF_SIZE_IN  MAX(4 * HS_PACKET_SIZE * NUM_USB_CHAN_IN, 4 * FS_PACKET_SIZE * NUM_USB_CHAN_IN_FS)
 
 /* Maximum USB buffer size (1024 bytes + 1 word to store length) */
 #define MAX_USB_AUD_PACKET_SIZE 1028
 
-#define OUT_BUFFER_PREFILL (MAX(NUM_USB_CHAN_OUT_FS*CLASS_ONE_PACKET_SIZE*3+4,NUM_USB_CHAN_OUT*CLASS_TWO_PACKET_SIZE*4+4)*1)
-#define IN_BUFFER_PREFILL (MAX(CLASS_ONE_PACKET_SIZE*3+4,CLASS_TWO_PACKET_SIZE*4+4)*2)
+#define OUT_BUFFER_PREFILL (MAX(NUM_USB_CHAN_OUT_FS*FS_PACKET_SIZE*3+4,NUM_USB_CHAN_OUT*HS_PACKET_SIZE*4+4)*1)
+#define IN_BUFFER_PREFILL (MAX(FS_PACKET_SIZE*2+4, HS_PACKET_SIZE*4+4)*2)
 
 /* Volume and mute tables */
 #ifndef OUT_VOLUME_IN_MIXER
@@ -41,10 +41,14 @@ static xc_ptr p_multIn;
 unsigned g_numUsbChanOut = NUM_USB_CHAN_OUT;
 unsigned g_numUsbChanIn = NUM_USB_CHAN_IN;
 
-#define MAX_DEVICE_AUD_PACKET_SIZE_CLASS_TWO ((MAX_FREQ/8000+1)*NUM_USB_CHAN_IN*4)
-#define MAX_DEVICE_AUD_PACKET_SIZE_CLASS_ONE (((MAX_FREQ_FS/1000+1)*NUM_USB_CHAN_IN_FS*3)+4)
+/* Note we could improve on this, for one subslot is set to 4 */
+#define MAX_DEVICE_AUD_PACKET_SIZE_MULT_HS  ((MAX_FREQ/8000+1)*4)
+#define MAX_DEVICE_AUD_PACKET_SIZE_MULT_FS  ((MAX_FREQ_FS/1000+1)*4)
 
-#define MAX_DEVICE_AUD_PACKET_SIZE (MAX(MAX_DEVICE_AUD_PACKET_SIZE_CLASS_ONE, MAX_DEVICE_AUD_PACKET_SIZE_CLASS_TWO))
+#define MAX_DEVICE_AUD_PACKET_SIZE_HS ((MAX_FREQ/8000+1)*NUM_USB_CHAN_IN*4)
+#define MAX_DEVICE_AUD_PACKET_SIZE_FS ((MAX_FREQ_FS/1000+1)*NUM_USB_CHAN_IN_FS*4)
+
+#define MAX_DEVICE_AUD_PACKET_SIZE (MAX(MAX_DEVICE_AUD_PACKET_SIZE_FS, MAX_DEVICE_AUD_PACKET_SIZE_HS))
 
 /* Circular audio buffers */
 unsigned outAudioBuff[BUFF_SIZE_OUT + (MAX_USB_AUD_PACKET_SIZE>>2) + 4];