Behavior Research Methods (2019) 51:204–234 https://doi.org/10.3758/s13428-018-1042-7 The Schultz MIDI Benchmarking Toolbox for MIDI interfaces, percussion pads, and sound cards Benjamin G. Schultz1 Published online: 17 April 2018 # The Author(s) 2018 Abstract The Musical Instrument Digital Interface (MIDI) was readily adopted for auditory sensorimotor synchronization experi- ments. These experiments typically use MIDI percussion pads to collect responses, a MIDI–USB converter (or MIDI–PCI interface) to record responses on a PC and manipulate feedback, and an external MIDI sound module to generate auditory feedback. Previous studies have suggested that auditory feedback latencies can be introduced by these devices. The Schultz MIDI Benchmarking Toolbox (SMIDIBT) is an open-source, Arduino-based package designed to measure the point-to- point latencies incurred by several devices used in the generation of response-triggered auditory feedback. Experiment 1 showed that MIDI messages are sent and received within 1 ms (on average) in the absence of any external MIDI device. Latencies decreased when the baud rate increased above the MIDI protocol default (31,250 bps). Experiment 2 benchmarked the latencies introduced by different MIDI–USB and MIDI–PCI interfaces. MIDI–PCI was superior to MIDI–USB, primarily because MIDI–USB is subject to USB polling. Experiment 3 tested three MIDI percussion pads. Both the audio and MIDI message latencies were significantly greater than 1 ms for all devices, and there were significant differences between percussion pads and instrument patches. Experiment 4 benchmarked four MIDI sound modules. Audio latencies were significantly greater than 1 ms, and there were significant differences between sound modules and instru- ment patches. These experiments suggest that millisecond accuracy might not be achievable with MIDI devices. The SMIDIBT can be used to benchmark a range of MIDI devices, thus allowing researchers to make informed decisions when choosing testing materials and to arrive at an acceptable latency at their discretion. Keywords Musical Instrument Digital Interface (MIDI) . Auditory feedback . Sensorimotor synchronization . Motor timing . Microcontrollers The Musical Instrument Digital Interface (MIDI) is a digital by performers from Prince to present-day bands like Snarky communication protocol for electronic musical instruments, Puppy, MIDI instruments have commonly been used in sen- computers, and audio devices that allows them to communi- sorimotor synchronization experiments to measure the timing cate between one another to produce music and sound effects of actions and to generate auditory feedback (cf. Repp. 2005; and to record responses. MIDI is, arguably, the most widely Repp & Su, 2013). In these experiments, participants aim to used technical specification for digital musical instruments, synchronize their responses to an external stimulus (e.g., a anditwaspopularevenbeforeitwasfirstpublished metronome or auditory sequence), and the timing of responses (International MIDI Association, 1983). Besides being used relative to events (or beats) is recorded. Despite the wide use and success of MIDI, the temporal latencies of the recorded Electronic supplementary material The online version of this article response timings and auditory feedback have rarely been (https://doi.org/10.3758/s13428-018-1042-7) contains supplementary benchmarked (but see Mills, van der Steen, Schultz, & material, which is available to authorized users. Keller, 2015; Repp, 2010; Schultz & van Vugt, 2016) and are rarely specified by the manufacturer. The aim of the pres- * Benjamin G. Schultz ent study was to describe tools to benchmark the latencies of [email protected] several commercially available MIDI devices—namely, the Schultz MIDI Benchmarking Toolbox (SMIDIBT). The 1 Basic & Applied Neurodynamics Laboratory, Department of Neuropsychology & Psychopharmolcology, Maastricht University, SMIDIBT affords the opportunity for researchers to measure Universiteitssingel 40, 6229 ER Maastricht, The Netherlands the timing error within MIDI devices (and configurations Behav Res (2019) 51:204–234 205 thereof), in order to make informed decisions regarding the study I also examined the performance of several affordable choice of experimental apparatus, sample sizes (and statistical devices—namely, an Alesis PercPad ($199 US), a LogiLink power, given said error), and interpretation of the results (e.g., MIDI–USB cable ($20 US), and a MIDItech Pianobox ($90 negative mean asynchrony; see Repp, 2005). US). I start by describing the hardware and software of the Previous sensorimotor synchronization experiments have SMIDIBT and exploring the limits of MIDI-based communi- used various combinations of MIDI response devices (e.g., cation (Exp. 1). I then investigate some of the assumptions pianos or percussion pads), MIDI-to-PC conversion interfaces surrounding the use of the MIDI protocols: specifically, USB (e.g., MIDI–USB converters), and external MIDI sound mod- polling rates, the asserted 1-ms resolution of MIDI devices ules to produce auditory feedback (see Table 1 and Fig. 1a). (e.g., Large, Fink, & Kelso, 2002; Ravignani, Delgado, & Similarly, the computer software used to record responses and Kirby, 2016), and whether MIDI messages and audio output control auditory feedback, such as FTAP (Finney, 2001)or are synchronous (see Maidhof, Kästner, & Makkonen, 2014). Max-MSP (Cycling’74, 2014), differs between studies. The present study compared the latencies of the various MIDI Although it would be difficult to benchmark some of these devices to the critical value of 1 ms, since this is the latency setups for various reasons (e.g., discontinued stock, financial assumed (and, perhaps, desired) in some experiments (e.g., expense, custom designs/scripts, PC specifications), it is pos- Large et al., 2002; Ravignani et al., 2016). The primary aim is sible to provide a benchmarking toolbox so researchers can to understand the hardware and software limitations that may test their own experimental setups. Here I present the influence latencies when using individual MIDI devices or SMIDIBT for MIDI devices and test some of the most fre- chaining several MIDI devices, and show users how to mea- quently used devices or the newer (or similar) versions (see sure these latencies themselves. To improve accessibility, I Table 1). Since Schultz and van Vugt (2016) claimed that one have also included a step-by-step guide in the supplementary of the advantages of an open-source microcontroller response materials (see the SMIDIBT Reference Manual) that contains device (other than sub-millisecond auditory feedback) is that less technical descriptions aimed at novices who perform au- it is more affordable than MIDI-based setups, in the present ditory feedback experiments. Table 1 List of the commercially available devices used in previous experiments and/or tested in the present study (demarcated with a *) Type Device References MIDI–USB interface LogiLink MIDI-USB* N/A M-Audio UNO* Mills et al. (2015) MIDI Man (MIDI Sport) Collyer et al. (1997); Schultz & van Vugt (2016) Roland UM-ONE* Rogers et al. (2014) MIDI–PCI interface Labway Soundboard D66* N/A Sound Blaster Live PCI* Pecenka & Keller (2011); Pfordresher & Benitez (2007); Pfordresher & Dalla Bella (2011); Pfordresher & Kulpa (2011) TerraTec TT Solo 1-NL* N/A Percussion pad Alesis PercPad* Sadakata et al. (2008) Roland Handsonic 20* (Roland Handsonic 10, 15) Hurley, Martens, & Janata (2014); Janata, Tomic, & Haberman (2012); Mills et al. (2015); Pecenka & Keller (2011); Schultz & van Vugt (2016) Roland SPD6* London et al. (2009); Pfordresher & Benitez (2007); Pfordresher & Dalla Bella (2011); Pfordresher & Kulpa (2011); Repp (2010); Repp & Knoblich (2007); Repp, London, & Keller (2005, 2012) MIDI sound modules MIDItech Pianobox* N/A Roland Mobile Studio Canvas SD-50* Pfordresher & Benitez (2007); Pfordresher & (Edirol StudioCanvas SD-80) Dalla Bella (2011); Pfordresher & Kulpa (2011) Yamaha TX81Z Schultz & van Vugt (2016) MIDI piano sound modules Kawai CL25* N/A Korg MicroX* N/A Roland RD-250s Repp (2010); Repp & Marcus (2010) Yamaha Clavinova CLP-150 Kaiser & Keller (2011); Pecenka & Keller (2011); Repp & Keller (2010); Repp, London, & Keller (2012) 206 Behav Res (2019) 51:204–234 Fig. 1 Layouts of a typical MIDI setup (a) and of the SMIDIBT setups sources of latencies in a typical MIDI setup is represented in panels b that can be used to test the latencies of MIDI messages that are sent (middle section of a typical MIDI setup), c (first section of a typical MIDI through computers and MIDI serial devices (b), the latencies of MIDI setup), and d (final section of a typical MIDI setup). The OUT audio and and audio from percussion pads (c), and the latencies of audio generated voltages can be compared in to her measure the veridical timing by MIDI sound modules (d). Each of the three components that can be between inputs and outputs MIDI-to-USB conversion and USB polling communication avoids the delays introduced by polling or, instead, introduces different or more variable delays (Finney, The speed at which MIDI messages can be sent and read by 2016). In Experiment 2 I benchmarked the latency introduced the USB port and other MIDI devices is determined by the by MIDI–USB and conventional Peripheral Component number of bits-per-second (bps), called the baud rate (or serial Interconnect (PCI) sound card interfaces, the latter requiring transfer rate). For MIDI, this