Heartbeat sound effects fall into the category of organic sounds that generally must be made with artificial means. This is because true human heartbeat sounds cannot be recorded easily. They are not loud enough through the human body to easily capture a strong recording. While some medical videos do demonstrate audio recorded in the human body, the recordings generally sound too muffled to be useful in film or video. Also, obviously, it is not easy, nor pleasant to stick a microphone into a human body. These types of medical mics and video equipment are obviously very expensive. However, even though these challenges exist, there are definitely many ways around them. And, professionals know the tricks of the trade certainly. Here at SFXsource we have talented sound designers who can artificially create heartbeat sound effects.
Since recording actual heartbeats can prove difficult to record with unsatisfying results, sound designers often turn to drum sounds for heartbeat sound effects. Generally a bass drum is the optimal choice for making a heartbeat sound effect because heartbeat sounds are low and pulsate in the same frequency as a bass drum, around 60-100 Hz. Once a good deep bass drum is chosen, the designer generally puts a high cut on all frequencies above 150 hz, because let's face it, there are not too many treble frequencies in heartbeat sounds. After this, a compressor is applied to the sound which gives a forceful pump and punch quality to the heartbeat. All professional sound designers at SFXsource.com use compression, Eq, and reverb consistently to enhance their audio offerings. Other sounds, though, can also be used. Any sort of forceful pound or drop sound can be edited and then looped to create the audio needed. For example, a heavy brick dropped on a towel on the floor will definitely give a sound designer the thud type impact sound needed. Or, hitting the flesh of ones fist on a hollow wood box will do the same trick. Really anything that can be recorded with has a good amount of low end and "punch" will provide the fodder needed to make heartbeat sound effects.
Once a recording has been made, or a drum sample chosen to build a heartbeat sound effect, the next step in the process is editing. For this type of sound, two samples must be taken from the recorded audio. This is because heart pumping sounds have a strong beat followed by a softer beat, which is a result of the retraction and release of this ever important human organ. The sound designer, after deciding which two samples to use, expertly cuts the two and then places them together on the timeline in their DAW. A new audio sample can then be bounced down to create a single two part Duh-DUH sound. Then, after ensuring that there is no clipping or bad sounds in the sample, the sound designer can loop the heartbeat sound effects to perfection, generally at 60-80 beats per minute as explained in this informative article, Heart Rate.
After the recording and editing process is completed., artificially created heartbeat sound effects are EQ'd and compressed by SFXsource.com sound designers, and slight delay (or better known as the echo effect to the layman) is applied for that "slapback" quality often heard in a heartbeat sound. If you think about it, a heart sound is not just a rhythmic "duh .. duh .. duh" but a "DUH-duh... DUH-duh...DUH-duh." It's the delay that gives the second "duh" to the human heart. The EQ is used to boost the lower frequencies and cut out any high frequencies. And, the compression gives the sound a strong pumping quality. Reverb, too, is almost always applied since it gives an airy quality to the heartbeat sound effects, making them both slightly muffled and dull, but pleasing to listen to.
Nicely, these heart audio clips, if done correctly, can be perfectly looped to any length needed by a filmmaker while editing. Filmmakers often use them in a way that conveys human emotion, either played slowly to demonstrate a relaxed character, or played fast to demonstrate stress of fear as in a thriller or horror film. Aside from using them in film or animation to add drama to a scene, they are also used in toys and baby products. For example, baby soothers which are attached to the sides of infant's cribs often include them as a choice of audio to relax babies while they fall asleep. In addition, they make good heartbeat sound effects ringtones. There is no limit on how they can be used, certainly. Hopefully this gives you, reader, a bit more understanding on how a sound designer creates heartbeat sound effects.