diff --git a/papers/format.md b/papers/format.md
index 2a0a045cf..b22d7b2c7 100644
--- a/papers/format.md
+++ b/papers/format.md
@@ -32,6 +32,7 @@ these fields are 0 in format versions prior to 100 (0.6pre1).
 
 the format versions are:
 
+- 158: Furnace dev158
 - 157: Furnace dev157
 - 156: Furnace dev156
 - 155: Furnace dev155
@@ -441,6 +442,9 @@ size | description
   4  | instrument directories
   4  | wavetable directories
   4  | sample directories
+ --- | **patchbay effects** (>=158)
+  2  | number of effects
+ 4?? | pointers to effects
 ```
 
 # patchbay
@@ -548,6 +552,31 @@ size | description
  1?? | assets in this directory
 ```
 
+# patchbay effect (>=158)
+
+these effects sit on the patchbay.
+
+```
+size | description
+-----|------------------------------------
+  4  | "EFFE" block ID
+  4  | size of this block
+  2  | slot
+     | - must be between 32 and 4092.
+     | - the other slots are reserved for chip/system portsets.
+  2  | effect ID
+     | - 0x00: dummy
+     | - 0x01: external (plugin bridge)
+     |   - not implemented yet
+     | - 0x02: volume
+     | - 0x03: filter (circuit)
+  4f | dry/wet balance
+  2  | reserved
+  2  | storage version
+  4  | storage length
+ ??? | storage data
+```
+
 # instrument (>=127)
 
 Furnace dev127 and higher use the new instrument format.