This master's thesis has a few interesting points http://www.inf.ufrgs..._UFRGS_2009.pdf
"[...] communications between the CPU and the GPU have a considerable time de-
lay. This can be observed both when launching GPU programs or when moving memory
between video memory and main memory. When developing a complex audio processing
application, one will likely desire to do the entire audio processing either on the CPU or
the GPU in order to minimize the number of memory transfers between CPU and GPU."
JOHNSON, 2005) and GPUs (GOVINDARAJU; MANOCHA, 2007)."
"Most of the works on GPU-based audio processing do not present a real-time application, and most also report little advantage of
GPU-based audio processing over a corresponding CPU-based one."
" Compared to the equivalent CPU-based technique using the same FFT op-
erations, this approach supports real-time processing of 2 to 4× more coefficients than it
was previously possible"
"Since larger speedups were expected, I have concluded that FFT algorithms, which are
frequently used for signal processing, benefit little of the GPU computing power, being
restricted by memory bandwidth and access patterns. It still makes sense, however, to im-
plement FFT-based processes on the GPU if they are combined with other processes that
do explore the GPU computational power, such as mixing, synthesis and non-recursive
"Using the FFT makes the method scale optimally for large recursive filters. However,
this kind of filter is very uncommon (the order of the recursive section is almost never
larger than 32 in typical audio applications). At such sizes, performing this filter on a
GPU is often slower than on a CPU"
It also cites a number of related articles if you want to read more about the topic.
My best guess is that we won't see this kind of thing in the near future, although I think dedicated DSP hardware
has been sold in the past, right? I'm just not sure who would be buying it.