Digital Turntable Setup DocumentationNathan Artz, Adam Goldstein, and Matthew PutnamAbstractAnalog turntables are expensive and fragile, and can only manipulate the speed of music without independently changing its pitch. Additionally, hardware and software for matching beats between songs are expensive and hard to use. The Digital Turntable Setup avoids these pitfalls by implementing frequency- and speed-adjusting features, along with beatmatching and echo and reverb effects, on a standard FPGA. The system’s behavior has been tested with music at multiple sampling rates.Table of ContentsList of Figures! 3Overview! 1Objective! 1Goals! 1Solution! 1Description! 2Overall Design! 2Input Methods (Adam Goldstein)! 3Turntable Input (Adam Goldstein)! 3Knobs (Adam Goldstein)! 5Keyboard (Matthew Putnam)! 5Sound Router (Adam Goldstein)! 6Phase Vocoder (Adam Goldstein)! 9Fixed Size Resampler (Adam Goldstein)! 11Memory (Nathan Artz)! 16Record Mode (Nathan Artz)! 16Playback Mode (Nathan Artz)! 17Write to Flash Mode (Nathan Artz)! 18Dual Read from Flash Mode (Nathan Artz)! 20Addresser (Adam Goldstein)! 21Beatmatcher (Adam Goldstein)! 24Audio Effects (Matthew Putnam)! 27Echo (Matthew Putnam)! 27Reverb (Matthew Putnam)! 28Testing and Debugging! 29Input Methods (Adam Goldstein)! 29Sound Router (Adam Goldstein)! 30Addresser (Adam Goldstein)! 31Beatmatcher (Adam Goldstein)! 31Memory (Nathan Artz)! 31Audio Effects (Matthew Putnam)! 32Conclusions! 34Acknowledgements! 34List of Figures1. " Overall design of the Digital DJ Setup" 22. " Operation of the Turntable Input" 43. " Signals through the Sound Router" 74. " Operations of the Sound Router" 85. " States of the Sound Router" 96. " Operation of the Phase Vocoder" 117. " States of the Phase Vocoder" 128. " Upsampling with the Fixed Size Resampler" 139. " Downsampling with the Fixed Size Resampler" 1510. High-level user memory diagram" 1611. Record modules" 1712. Utilization of a ZBT RAM slot" 1813. Write to flash FSM" 1814. Flash memory allocation" 1915. Timing of ZBT/flash copy" 2016. Memory module visualization in write-to-flash mode" 2117. Dual flash read FSM" 2218. States of the Beatmatcher" 2619. FFT debugging" 3020. Addresser debugging" 3221. Beatmatcher debugging" 32OverviewObjectiveThe Digital DJ Setup attempts to provide features to help a DJ play two tracks of music while adjusting the pitch and speed in various ways to make the music more danceable or fun to listen to.GoalsThe goals of the system are:•To record two tracks of music and play them back either one at a time or together•To adjust the pitch of music, either live or recorded, with a knob•To implement a “turntable” whose rotational speed determines the pitch or speed of the music•To adjust the pitch of music at standard harmonic intervals using a computer keyboard•To match the beats of two songs, slowing down or speeding up one as necessary•To add echo and reverb effects to music•To record the results of mixing into storage to make it possible to layer mixesSolutionThe proposed system achieves the above goals through use of a modular hardware design. The system uses sophisticated memory architectures to record tracks as they arrive from an audio input, and to store them permanently in flash memory. Additionally, the memory architecture allows music to be recorded to memory as it is played back, making it easy to iteratively record several layers of music on top of each other.Additionally, the design makes it possible for the user to choose whichever human interface he prefers; since all human interfaces output a sampling ratio, they require no internal changes to be switched from being used to adjust speed (resampling in the time domain) to being used to adjust pitch (resampling in the frequency domain).The pipelined nature of the design allows effects like echo and reverb to be added to the “chain” of audio samples traveling through the system, smoothly integrating them with other effects like pitch- and beat-matching.Digital DJ Setup Documentation! 1DescriptionOverall DesignThe Digital DJ Setup comprises several interacting subsystems (Figure 1). First are the human interfaces, including a knob, a turntable, and a computer keyboard. These produce sampling ratios that can be used to adjust the pitch or speed of music.Second is the pitch-adjusting subsystem, encapsulated in the Sound Router, that provides near-real time transposition of music.Third are the Beatmatcher and Addresser, which let the user input the speeds of two different songs and have the song playback speed matched.Digital DJ Setup Documentation! 2Pitch KnobTurntableKeyboardBeatmatcherSelector (conceptual)Sound RouterPitch sampling ratioSound inAddresserPitch-adjusted sound outTime sampling ratioSelector (conceptual)Time sampling ratioTime samplingratioForce overrideMemoryAddressSpeed-adjusted sound outFigure 1: The overall design of the Digital DJ Setup. In practice, the “selectors” were not included; rather, the modules on the left were wired directly to the desired modules on the right.Fourth is the memory subsystem, which handles the details of recording music and playing it back.The final subsystem handles audio effects like echo and reverb, applied to the output of all the previous subsystems. All of these subsystems and their interactions are described below.Input Methods (Adam Goldstein)There are a number of ways of inputting settings into the system to change pitch, playback speed, and volume.Turntable Input (Adam Goldstein)One of the primary ways to input speed or pitch information into the system is using a “turntable”—a motor connected to a rotary encoder with a protruding plate. The Turntable Input module makes it possible to set a reference speed for the turntable. Later, when the turntable is spun faster or more slowly, Turntable Input produces a sampling ratio of two four-bit numbers that will cause the Addresser to change playback speed proportionally to the change in the turntable’s rotational speed. (For instance, if the turntable were spun 50% more slowly than its reference speed, the sampling ratio would be 2/1, so playback would proceed at 50% its normal speed.)In addition, Turntable Input determines the direction in which the encoder is spinning, and produces an output (clockwise) that represents the direction of rotation. This can be connected directly to the Addresser’s read forward input to ensure that changing the direction of turntable rotation
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