← SensorSynthFMSensorSynthFM is an iPad-native FM instrument shaped by touch, device motion, microphone energy, and environmental signals. The current milestone is a one-screen instrument where source, amount, destination, live response, and zero state are all audible, visible, controllable, and recoverable. The build runs on hardware, survives its own walkthrough in seven of eight steps, and has a specific, documented list of what it still gets wrong. This page is the synopsis. The dated history, with every failure in order, lives in the full build log linked at the bottom.
A note on process. The code is written with AI assistance. I set the product direction, made the musical and interface judgments, ran every physical test described here, and I own every claim on this page.
What Works on the iPad
The accepted July 22 build passed 22 automated Xcode tests and a generic iOS build, then signed, installed, launched, and ran on my 11-inch iPad Pro. When the seven-day development signing profile later expired, a fresh Xcode run signed and installed the same build and it launched again. That interruption was a signing failure, not a product-code failure, and it is worth naming because build history should distinguish the two.
On August 3 I ran an eight-step cognitive walkthrough on the physical iPad, testing the instrument the way a first-time user would encounter it. Seven steps passed:
- Play was visible.
- Sound started, and the playing state made sense.
- The active source and FM destination were clear.
- Manual control and sensor modulation were distinguishable from each other.
- Microphone response was visible and audible.
- Setting a route to zero neutralized it, and restoring the amount resumed modulation.
- I could explain the premise of the instrument in one sentence.
The sensor mappings themselves earned their place through direct testing. Accelerometer magnitude routed to modulation index at +40 percent produced a clear change when the device moved; table taps and stationary vibration did not produce a useful result, which sets a real boundary on what the mapping is for. Gyroscope Y routed to modulator ratio at +41 percent changed timbre and apparent pitch predictably under slow tilting. Microphone amplitude routed to amplitude at +63 percent behaved the way an instrument source should: a quiet tone stayed stable, speech raised loudness proportionally, and claps produced louder transients with a slight apparent delay. That source is worth keeping if it is programmed and limited carefully.
There is also a handedness switch that moves auxiliary controls for left- and right-handed use. It works mechanically. It has not been tested with left-handed users, so I make no claim beyond the mechanism.
What the iPad Rejected
The eighth walkthrough step failed, and the failure is the most important finding in the current build. Accelerometer modulation changed the sound with no detectable visual response. Gyroscope response was visible but too subtle to trust. The screen did not adequately show what the sensors were doing to the sound. For an instrument whose whole premise is sensor modulation, that is not a cosmetic gap. It is the core promise going unexplained on screen.
The layout has a related problem: the full nine-source matrix still requires horizontal scrolling, which means part of the instrument is off screen at any given moment.
The walkthrough also exposed a discoverability failure in routing. Selecting a zero-valued route cell did not show the route as active. The route only became apparent after the amount moved away from zero. The interface did not explain how to create a route or how to remove one. I could operate it because I built it. A new user would have no such advantage.
What Changed Because It Failed
Every major decision in this build traces to a physical failure, not to a preference. Earlier rounds on hardware produced their own corrections. System chrome, meaning the iPad status area and gesture regions that surround the application, covered controls in an early layout. The first route editor collided with the iPadOS bottom gesture zone. Microphone behavior was too subtle to trust. Fixed routing hid the range of the instrument. Sensor writes made manual controls look broken. A side panel made the primary amount control too narrow, and the native layout hid the ninth source entirely. Each of those failures forced a design change that survives in the current build.
The August 3 walkthrough adds a new required list:
- Selected zero routes stay visibly selected.
- The interface explains that moving the amount activates a route.
- Every active route gets a visible X or remove control. Double-tap may remain a shortcut, but it cannot be the only removal method.
- Sensor response is shown clearly, so the ear and the eye agree.
- All nine sources fit on screen without shrinking touch targets.
What does not change: familiar synthesis controls, bipolar amounts, a visible zero state, large touch targets, and clear source-to-destination routes. Those are the parts the walkthrough validated, and they hold.
Requirements Under Test
SensorSynthFM is now built and judged under a managed requirements method. The method comes from Jeremy Dick, Elizabeth Hull, and Ken Jackson, Requirements Engineering, Fourth Edition. It separates stakeholder outcomes in the problem domain from system behavior in the solution domain, and it gives every managed requirement a source, a rationale, requirement attributes, a qualification method, and traceability through implementation and evidence. The organizing question is not whether the feature was built. It is what would convince the stakeholder that the requirement has been satisfied. A passed implementation test does not by itself qualify a stakeholder outcome, so passing code and satisfied requirements remain separate claims. Official book page.
What follows is a readable public projection of a fuller requirements record. Stable requirement IDs now travel through the working task board and the dated public history, so a decision made today can be traced back to the requirement it answers. The current evidence comes from one expert maker on one physical 11-inch iPad Pro, including the August 3 eight-step walkthrough in which seven steps passed. It is not outside-user validation.
Every enabled sensor route must make source, amount, destination, live response, and neutral zero state audible and visible.
- Why it exists
- Sensor modulation is the instrument's central promise. Audible change without visible cause reads as random or broken.
- Qualification
- On the physical iPad, isolate a route, create a source change, and identify source, destination, direction, and visible response before explanation.
- Current evidence
- Microphone response passed; accelerometer response was not visibly detectable; gyroscope response was too subtle to trust.
A selected route at zero must remain visibly selected and explain that changing the amount activates modulation.
- Why it exists
- Zero is an editing state, not the absence of a selection.
- Qualification
- Starting at zero, identify the selected route and the activation action without prompting.
- Current evidence
- The selected zero route did not look active, and the interface did not explain route activation.
Every active route must provide a visible, accessibly named removal control and a straightforward recovery path.
- Why it exists
- A shortcut gesture may help, but it cannot be the only way to remove a route.
- Qualification
- Remove and restore a route without being told a hidden gesture.
- Current evidence
- The removal control and recovery path are specified, but they have not been qualified on the current build.
The landscape modulation surface must keep all nine current sources available without shrinking route cells below the accepted 56-point touch baseline.
- Why it exists
- The matrix cannot solve fit by making the instrument harder to touch.
- Qualification
- On the 11-inch iPad in landscape, verify all nine sources, four destinations, and route editing are reachable, and measure every route cell.
- Current evidence
- The ninth source requires horizontal scrolling.
Manual base values and live sensor contribution must remain distinct, and returning a route to zero must neutralize sensor contribution without destabilizing sound.
- Why it exists
- The musician needs control authority and recovery.
- Qualification
- Move a route through positive, zero, and negative amounts while comparing base and live values and checking sound stability.
- Current evidence
- Passed James's owner-operated walkthrough; no outside-user evidence exists.
Microphone modulation must remain visibly and audibly causal while quiet input stays stable and louder speech or transients increase response without runaway pumping for two minutes.
- Why it exists
- Environmental input should shape sound without taking over the instrument.
- Qualification
- Record quiet baseline, speech, and clap response on the physical iPad for two minutes, and judge causality, stability, pumping, delay, and musical usefulness.
- Current evidence
- Passed one maker-operated test; exact calibration and transient delay remain open.
Before note-entry code is accepted, the interaction specification must define pitch mapping, touch-to-sound timing, polyphony, multi-touch, pressure or area, glide, scale and range behavior, handedness, feedback, accidental activation, recovery, accessibility, and explicit non-goals.
- Why it exists
- SensorSynthFM must become a playable instrument without turning a solution idea into an unexamined requirement.
- Qualification
- Review every named attribute, source, edge case, rejected alternative, and physical acceptance test before implementation.
- Current evidence
- The interaction specification gate is accepted; note-entry behavior is not yet qualified.
Three of the seven are failed on the current build, two are accepted and unqualified, and two hold on evidence produced by one maker on one device. Those numbers are the honest state of the instrument today, and they stay on this page until the evidence changes them.
The Next Field Pass
The next outside research idea is a visit to an Apple Store to study how users naturally approach and use display iPads. The questions are basic and directly relevant to this instrument: portrait versus landscape, where the first touch lands, one-hand versus two-hand use, reach, grip changes, keyboard and stand use, and how users recover from confusion. An instrument that lives on a tablet should be shaped by how users actually hold tablets, not by how I hold mine.
The first visit is only to understand the setting. Before any formal observation, I will settle the research boundary and obtain any required store permission. I will not record names, demographics, photos, audio, video, or quotes, and I will not interrupt anyone. That is the limit of what is planned.
Current Boundary
Every result on this page comes from one user testing on one device. The walkthrough, the mapping passes, and the failures are all mine, on my iPad. That is enough to drive design, and it is not enough to validate it. The handedness switch is untested with left-handed users. The discoverability fixes are specified but unproven. The project still needs testing with users other than me, and until that happens, the claims here stay scoped to what I observed directly.
Links
- Full build history, the dated log of every build, failure, and correction
- Desk research, the background work on FM synthesis and touch instruments
- Interactive layout study, the browser-based exploration of the one-screen layout
- GitHub, the source repository
The next commitment is specific: keep routing visibility open, make sensor response legible on screen, fit all nine sources without shrinking a single touch target, and put the result back on the physical iPad to fail or pass in the open. Consequential work keeps its requirement ID, qualification test, and evidence state as it moves through implementation and the dated history. The routing visibility and physical-iPad gates remain open.