52 Karplus-Strong String Synthesis

52 : Karplus-Strong String Synthesis

How it works

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 Frame

SPI Mode: CPOL = 0, CPHA = 1

The 16-bit SPI frame is defined as,

$\text{Read}/\overline{\text{Write}}$ $\text{Address[6:0]}$ $\text{Data[7:0]}$
Register Map

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.

I2S Transmitter

The 8-bit signed sound samples can be read out at f_sck = 256 kHz through this interface.

How to test

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