What's the best way to read analogue input using GPIO?

I'm reading the Sparkfun sound sensor amplitude/envelope which is analogue. The sensor doesn't seem to have I2C sadly. I think I could use SPI instead, but is there an easier way to read this data that I'm missing? Also, do you NEED a MCP3008 to read the data? Link to the sensor: https://learn.sparkfun.com/tutorials/sound-detector-hookup-guide#software-example