Creating knife slash sound effects
We’ve recently been asked to produce a set of 4 different knife slash sounds, with the requirement being the knife must cut the flesh with a nasty fleshy blood squelch. So we thought we’d write a short article on how we achieved this. In the real world, such an action would likely not produce much of a sound at all. But Hollywood has dramatised actions such as this and added an exaggerated element, so what we now expect this to sound like is completely different to how it really would.
Typically, when the sound of a knife cutting (mainly for fight scenes or other weapon sounds) is required, Foley artists use the sound of the metal blade slicing against another hard surface, such as a rock, concrete or another knife blade. This gives the exaggerated metal slice we would all recognise. So, first up I used a large kitchen knife and recorded the action of it slicing against a marble worktop and another knife for good measure.
Next up I needed a harsher skin slice sound. Again this wouldn’t usually produce much of a sound in real life, however movie goers expect to hear an exaggerated version. So to achieve this I recorded the sound of the knife cutting various vegetables. These included peppers, chillies, potatoes and some lettuce. I mixed these together adjusting the levels to get the right sound and bounced them down to individual files for mixing with the other sounds later.
Now for the really fun part… The guts, blood and fleshy sound. This is a messy job but one that’s really enjoyable. From past experience I know that stodgy rice, jelly and water mixed with cornflour all mixed together can produce a lovely fleshy sound, so I used all three and mixed them together. I recorded several versions and again bounced them down, ready for mixing with everything else later.
The final mix
Now I had all three elements of each slice sound ready to go. The knife slicing against metal and marble, the skin slice sound using vegetables and the fleshy blood and guts sound using jelly, rice and water with cornflour. I assigned a track in Logic for each take. Then I dragged the bounced versions for each session onto a stereo audio track and applied a small amount of compression on each. I used Logics slice tool to split the audio regions for each take and align them up so each of the sounds would play together. It often takes a bit of playing around with timings an audio levels to get the right sound and going on the specifications the user had given me I did my best to match the sounds.
I found that you get a better sound if the knife slice sound happens first, dry, with the skin slice sound very slightly delayed after, then the wet, squelchy guts sound coming in around half way and trailing off on its own. However this is a personal choice and one that you’ll likely have your own preference for.
You can preview and download the final results mp3 or wav files here: