![]() Afterwards we developed a new firmware, guided by recorded sensor data and host-based simulation. Because the Uno lacks native USB, a serial->MIDI bridge process had to run on the PC. The system tested by users was running the very first hardware and firmware version. With simulation-hardened Arduino firmware The latter can quickly be come significant at 4 meters the delay is already over 10 milliseconds.Īnd at this time, we know what the total latency is, but don’t have information about how it is divided. The capacitive effect that the sensor relies on will have a non-zero response time, and it takes time for sound played by the speakers to reach our ears. There are also sources of latency outside the software and electronics of the system. However usually a large portion of the time is spent in a small parts of the system, so an important part of optimization is to locate the areas which matter (or rule out areas that don’t).įor the MIDI controller system in question, a software-centric view looks something like:Ī functional view of the system and major components that may contribute to latency. Latency, like other performance issues, is a compounding problem: Each operation in the chain adds to it. Since the instrument in question is going to be a kit targeted at hobbyists/amateurs, we decided on an initial target of <30ms. With latency, musicians execute their gestures ahead of theīeat to align the sound with a metronome, and that theyĬan maintain synchronisation this way up to 55ms latency. Instruments should aim for latency less than 10ms ĭahl and Bresin found that in a system Wessel and Wright suggested that digital musical From Action-Sound Latency: Are Our Tools Fast Enough? ![]() ![]() So the latency experienced would offset the sound by more than one 16th note! We can understand that this would make it tricky to play.įor professional level audio, less than <10 ms is a commonly cited as the desired performance, especially for percussion. In the following soundclip the kickdrum is playing 4/4 and the ‘ping’ all 16 16th notes. For reference, when playing a (relatively slow) 4/4 beat at 120 beats per minute, the distance between each 16th notes is 125 ms. We now know that the latency experienced by our testers was around 137 ms. Raw sound data, data with normalized amplitude and measured distance between the sound of tapping the sensor and the sound coming from speakers. And then we can manually select and label the distance between the starting points of the sounds to get our end-to-end latency. Using Effect->Amplify to normalize the audio to -1db makes it easier to see the waveforms. Then we open the video in Audacity audio editor to analyze the results. For synthesizing sounds from the MIDI signals we use LMMS, a simple but powerful digital music studio. Setting a low video bitrate to save space, and enabling macro-mode for focusing close objects easier. To get access to more settings, the open-source OpenCamera Android app was used. The synthesized sound was chosen to be easily distinguished from the thud of the controller pad.In case the images are useful for understanding the recorded test, video is also recorded.Volume of the output was adjusted to be roughly same level as sound of physically hitting the pad.The controller pad is tapped with the finger quickly and hard enough to be audible.The microphone is positioned close to the controller pad and the output speaker.Test setup for measuring MIDI controller end2end latency using audio recorded with smartphone. Instead we decided to go with a purely audio-based method: So to find when pad was hit with higher accuracy (1ms) would require using multiple frames and interpolating the motion between them. However even at 120 FPS, which some modern cameras/smartphones can do, there is 8.33 ms per frame. My first idea was to use a high-speed camera, using the video image to determine when pad is hit and the audio to detect when sound comes from the computer. ![]() And to have concrete, objective data to go by, we need to measure it. So this is what we must be able to observe in order to evaluate current performance and the impact of attempted improvements. For a MIDI controller that means the end-to-end latency, from hitting the pad until the sound triggered is heard. ![]() Testing latencyįor an interactive system like this, what matters is the performance experienced by the user. A synthesizer on the computer turns the notes into sound. An Arduino board processes the sensor data and sends MIDI notes over USB to a PC or mobile device. Dhang: A MIDI controller using capacitive touch sensors for triggering. ![]()
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