Inside the DGX digital pianos

Thanks to SeaGtGruff in the PSR Tutorial Forum, I took a chance to deep dive a few members of the Yamaha DGX portable grand family. The DGX is a “value” line of electronic keyboards offering a digital piano experience at affordable prices.

Polyphony depends on the available processing power and memory bandwidth (i.e., the ability to transfer samples from wave memory to the processing elements).

Here is a small table for some models in the DGX product line. I took a look at the service manual for models with distinctive features, e.g., DSP effects or no DSP effects. The analysis came out rather nice, so I decided to post it here, too.

           Poly Panel XGlite Kits REV CHO DSP IntMem  Processor
           ---- ----- ------ ---- --- --- --- ------  ------------------
DGX-200     32   108   480    12    8   4   0  352KB
DGX-300     32   122   480    12    8   4  38
DGX-500     32   122   480    12    8   4  38         HG73C205AFD SWX00B
DGX-520     32   127   361    12    9   4   0  875KB
DGX-530     32   127   361    12    9   4   0  875KB  YMW767-VTZ  SWL01T
DGX-620     32   127   361    12    9   4   0  875KB
DGX-630     64   130   361    12   29  24 182 1895KB
DGX-640     64   142   381    12   35  44 238 1895KB  R8A02032BG  SWX02
DGX-650    128   147   381    15   35  44 237  1.7MB  R8A02042BG  SWX08
DGX-660    192   151   388    15   41  44 237  1.7MB

Yamaha has several proprietary processors. The least powerful are the SWLs, which are normally used in the entry-level portables. The SWL does not have DSP support for variation/insert effects. Samples are transfered on the same bus as CPU instructions — low bandwidth. SWLs make for inexpensive products, but no DSP effects and relatively low polyphony.

The PSR E-series typically uses SWL01 variants such as the SWL01U in the PSR-E443. It’s interesting that the DGX members using the same SWL01 processor do not have DSP effects. The SWX processors have integrated DSP capability; the SWLs do not.

The SWX family of processors have dedicated buses/memories and a hardware digital signal processor for effects. (I deliberately avoided the acronym “DSP” here to avoid confusion with the way “DSP” is used in arranger terminology.) The SWX08 has three dedicated buses and memories:

  • SHA2 CPU bus and memory (CPU program and data)
  • Wave ROM bus and memory (voice samples)
  • DSP RAM bus and memory (working memory for digital signal processing)

The extra memory and external connections increase cost. However, this is a lot more processing power and memory bandwidth than the lowly SWL!

The SWX00 and SWX02 are earlier members of the family and aren’t used in new designs anymore. It’s too soon to see a service manual for the DGX-660, so any further comment is an educated guess. I suspect an SWX08 operating at a higher clock rate.

The SWX08 is used in the PSR-S750 and the SWX02 is used in the MOX. In both of these cases, the SWX is the main CPU and tone generation is handled by a single SWP51L tone generator chip, not the SWX. Because Yamaha had its own internal IC fab then these products were designed, Yamaha incorporated its own proprietary processor instead of an off-the-shelf Renesas R8. This is an effort to increase Yamaha’s own fab volume. Yamaha may even be using SWX chips in which the processor is good and the DSP is faulty and fused out!

Analysis isn’t complete without looking at wave memory size:

Model   Wave memory                Size         Description
------- -------------------------- ------------ ------------------------
DGX-500 K3N7V402GB-DC10            64Mbit  8MB  Mask ROM 64Mbit (wave)
DGX-530 Lapis Semi MR27V12852L     128Mbit 16MB 8Mx16b P2ROM (prog+wave)
DGX-640 Lapis Semi MR27V12852L     128Mbit 16MB 8Mx16b P2ROM (wave)
DGX-650 Spansion S29GL256S90TFI020 256Mbit 32MB 16Mx16b NOR flash (wave)

Memory size affects the number and quality of the voices. More memory allows more voices, more samples per voice, longer samples per voice, etc. Pianos are especially memory hungry. So, improvements in piano voices usually require significantly more wave memory. SWX wave memory is 16-bits, data parallel.

Now that Yamaha have sold off their IC fabrication capability, they aren’t under the same pressure to use proprietary processors. It’ll be interesting to see if Yamaha adopt ARM for tone generation and/or effects in value product lines. In the Reface line, they have adopted ARM for user interface and control. Yamaha’s Mobile Music Sequencer on iPad has a fairly completely XG engine, so Yamaha certainly aren’t strangers to tone generation on ARM!

If you enjoyed this article, you might also like this overview of the Tyros/PSR arranger family architecture.