Serial memory and tone generation

Ah, September. Soon it will be time to speculate about new products at the Winter 2016 NAMM!

Every now and again, I take a pass through recent patent filings from Yamaha to get an idea about future product developments. Of course, the tech in a filing may never make it to product. However, a few common threads begin to appear over time.

This post starts with a patent application having the inauspicious title, “Sound Generation Apparatus.” This US application 2014/0123835 was filed on November 5, 2013 and is based on Japanese patent -244002, which was filed November 5, 2012.

First, a little background about the Yamaha tone generation architecture. Yamaha has used the same overall architecture for mid- and high-end workstations and tone modules since the mid-1990s. (TG-500, anyone?) These products employ one or more large scale integrated circuits for tone generation. Current versions of the tone generator IC, the SWP51L, has two dedicated memory channels for waveform data. Each channel has a 16-bit parallel data bus and a parallel address bus (24 or more bits wide). The parallel interface takes at least 40 pins per channel.

That’s a lot of incoming and outgoing connections (80 plus pins for both channels). IC packaging costs are in the range of $2.50 USD to $4.50 per pin. So, there is a direct relationship between the number of IC pins and manufacturing cost. Ultimately, this cost has a real effect on profit and the final price of the product.

The Yamaha patent application describes a serial interface for waveform memory in place of a parallel interface. The serial interface requires six pins per channel. Instead of 80 pins, the serial interface approach uses only 12, providing an 8 to 1 savings in packaging costs alone.

The application cites the Winbond 25Q series as the kind of flash memory to be supported by the serial interface. The largest 25Q device has a 64MByte capacity and can sustain a 40MByte/second transfer rate (quad SPI mode). This is nearly sufficient bandwidth to drive 128 44,100Hz stereo polyphonic voices (about 45MBytes/sec).

If you do the math that’s 128 times 44,100Hz times eight bytes. Two successive samples are required in order to perform interpolation although the oldest sample could be cached.

The product implications are interesting. At the low end of the scale (one or two channels), the device footprint is much smaller. The small size allows a corresponding decrease in the size of the product. Maybe a guitar pedal stomp box?

The high end of the scale is more intriguing. It becomes possible to build a tone generator IC with four or even eight independent channels of tone generation where each channel is driven by its own memory stream. We’re talking 1,024 polyphonic voices in the same LSI footprint as today’s SWP51L.

There are design implications for entry-level keyboard products, too. The SWL01 system on a chip (SOC) integrates both CPU and tone generator onto the same IC. Waveform data (samples) travel on the same bus as CPU instructions and data. A serial SPI interface requires only six pins and might let designers shift waveform storage from ROM on the system bus to a dedicated memory bus and channel. Software might be able to perform new tasks such as variation effects with more bandwidth available to the CPU on the system bus.

I feel confident to predict that the next generation of Standard Wave Processor (SWP) is in development. The SWP51L has been around for a while (including Tyros5). Here are a few key products and members of the SWP50 family:

    Product   Year  TG chip
    --------  ----  -------
    Tyros     2002  SWP50
    Motif XS  2007  SWP51
    Tyros 3   2008  SWP51B
    Tyros 5   2013  SWP51L

It is definitely time for a new design, not an incremental refresh.

Yamaha sees its internal integrated circuit capability as a strategic advantage. Up to this point, Yamaha have both designed and fabricated its own ICs. Last year, Yamaha transferred its fabrication line to Phenitec Semiconductor. Yep, Yamaha has gone fabless. This gets a huge capital expense off its balance sheet. It also means that Yamaha is under less pressure to reuse the same parts across product lines in order to get its IC manufacturing volume up. This is one reason why the SWP51 has had such long legs and why the SWL01 is used across all of the E-series arrangers. Volume, volume, volume! The pressure to (re)use Yamaha’s own IC solutions has been reduced.

We’ll see if Johnny can read (defenses) against Dick LeBeau. Go Browns!