This is simplified implementation of Karplus-Strong (KS) string synthesis based on papers, Digital Synthesis of Plucked-String and Drum Timbres and Extensions of the Karplus-Strong Plucked-String Algorithm.
A register map controls and configures the KS synthesis module. This register map is accessed through a SPI interface. Synthesized sound samples can be accessed through the I2S transmitter interface.
SPI Mode: CPOL = 0, CPHA = 1
The 16-bit SPI frame is defined as,
| $\text{Read}/\overline{\text{Write}}$ | $\text{Address[6:0]}$ | $\text{Data[7:0]}$ |
|---|
The Register Map has 16 Registers of 8-bits each. It is divided into configuration and status registers,
Complete register map is described in the repository at https://github.com/pyamnihc/tt04-um-ks-pyamnihc.
The 8-bit signed sound samples can be read out at f_sck = 256 kHz through this interface.
Connect a clock with frequency f_clk = 256 kHz and apply a reset cycle to initialize the design, this sets the audio sample rate at fs = 16 kHz. Use the spi register map or the ui_in to futher configure the design. The synthesized samples are sent continuously on the I2S transmitter interface.
| # | Input | Output | Bidirectional |
|---|---|---|---|
| 0 | ~rst_n_prbs_15, ~rst_n_prbs_7 | segment a | sck_i |
| 1 | load_prbs_15, load_prbs_7 | segment b | sdi_i |
| 2 | freeze_prbs_15 | segment c | sdo_o |
| 3 | freeze_prbs_7 | segment d | cs_ni |
| 4 | i2s_noise_sel | segment e | i2s_sck_o |
| 5 | ~rst_n_ks_string | segment f | i2s_ws_o |
| 6 | pluck | segment g | i2s_sd_o |
| 7 | NOT CONNECTED | dot | prbs_15 |