rickman wrote in :

You posed a problem; I gave you an answer. BTW there cannot be an
easier item to lash to a microcontroller than a DDS

Thank you for your suggestion.


Assuming that DDS is Direct Digital Synthesis, I'm not sure anything needs to
be lashed to anything. Just use a phase accumulator in a single DWORD or
whatever native data size gives adequate resolution. Then just feed a DAC,
assuming the processor has one. I think very many of them do.

On 09/10/2014 20:21, Lostgallifreyan wrote:
rickman wrote in :

You posed a problem; I gave you an answer. BTW there cannot be an
easier item to lash to a microcontroller than a DDS

Thank you for your suggestion.


Assuming that DDS is Direct Digital Synthesis, I'm not sure anything needs to
be lashed to anything. Just use a phase accumulator in a single DWORD or
whatever native data size gives adequate resolution. Then just feed a DAC,
assuming the processor has one. I think very many of them do.


Fine, but first find a microcontroller with such a fast (minimum 60MHz)
DAC. Even if you do you'll spend many times the cost of a simple
microcontroller plus DDS chip system - and you won't rival the cheaper
system's performance until your DAC can work at several times 60MHz.

PA

Peter Able stuck@home wrote in news:ks2dncC5fJrIAqrJnZ2dnUVZ7s-
:

Fine, but first find a microcontroller with such a fast (minimum 60MHz)
DAC. Even if you do you'll spend many times the cost of a simple
microcontroller plus DDS chip system - and you won't rival the cheaper
system's performance until your DAC can work at several times 60MHz.


Good point. Almost certainly easier to just send step size from CPU to the
accumulator in fast hardware. The step size needs changing far less often
than it needs stepping.

Lostgallifreyan wrote:
Peter Able stuck@home wrote in news:ks2dncC5fJrIAqrJnZ2dnUVZ7s-
:

Fine, but first find a microcontroller with such a fast (minimum 60MHz)
DAC. Even if you do you'll spend many times the cost of a simple
microcontroller plus DDS chip system - and you won't rival the cheaper
system's performance until your DAC can work at several times 60MHz.


Good point. Almost certainly easier to just send step size from CPU to the
accumulator in fast hardware. The step size needs changing far less often
than it needs stepping.

That is what the external DDS chip is doing.

When you require only FM-modulated signals and no sinewave, existing
microcontrollers can do it using their onboard timers and programmable
clock dividers. For example, the Raspberry Pi has been turned into
FM-broadcast and amateur radio shortwave FSK/ASK transmitter, the RF
signal appears (as a square wave) directly on a GPIO pin. Just filter
and amplify, or when you don't ca just connect a random wire as an
antenna to transmit a couple of mW (and harmonics).

Rob wrote in
:

Lostgallifreyan wrote:
Peter Able stuck@home wrote in news:ks2dncC5fJrIAqrJnZ2dnUVZ7s-
:

Fine, but first find a microcontroller with such a fast (minimum
60MHz) DAC. Even if you do you'll spend many times the cost of a
simple microcontroller plus DDS chip system - and you won't rival the
cheaper system's performance until your DAC can work at several times
60MHz.


Good point. Almost certainly easier to just send step size from CPU to
the accumulator in fast hardware. The step size needs changing far less
often than it needs stepping.

That is what the external DDS chip is doing.

When you require only FM-modulated signals and no sinewave, existing
microcontrollers can do it using their onboard timers and programmable
clock dividers. For example, the Raspberry Pi has been turned into
FM-broadcast and amateur radio shortwave FSK/ASK transmitter, the RF
signal appears (as a square wave) directly on a GPIO pin. Just filter
and amplify, or when you don't ca just connect a random wire as an
antenna to transmit a couple of mW (and harmonics).


An off-topic question, but very interesting at least to me... Do DDS chips
exist with 128 or even 256 phase accumulators onboard with the step size
adjustment being capable of matching the speed of the stepping itself
(though taking external control of local phase modulations between
accumulators), and allowing mixing of all outputs, perhaps in user-selected
groups based on binary fractions of the total accumulator count?

I ask because if they do it might be possible for me to convert my phase mod
synth code to dedicated hardware without resorting to very fast CPU's...
While the rates are audio only, the huge parallel array gets demanding of CPU
time as it is.

I suspect the answer to all that may be 'no' without custom VLSI chips
because of the relatively complex paths between accumulators needed for a
phase mod synth of N operators per algorithm, but maybe DDS chips come in
enough varieties to surprise me.

Lostgallifreyan wrote:
An off-topic question, but very interesting at least to me... Do DDS chips
exist with 128 or even 256 phase accumulators onboard with the step size
adjustment being capable of matching the speed of the stepping itself
(though taking external control of local phase modulations between
accumulators), and allowing mixing of all outputs, perhaps in user-selected
groups based on binary fractions of the total accumulator count?

I ask because if they do it might be possible for me to convert my phase mod
synth code to dedicated hardware without resorting to very fast CPU's...
While the rates are audio only, the huge parallel array gets demanding of CPU
time as it is.

I suspect the answer to all that may be 'no' without custom VLSI chips
because of the relatively complex paths between accumulators needed for a
phase mod synth of N operators per algorithm, but maybe DDS chips come in
enough varieties to surprise me.

You can do this with an FPGA. That is a programmable VLSI chip that
you program yourself to perform the functions you need. It operates
at logic speed, not at processor speed.

Rob wrote in :

You can do this with an FPGA. That is a programmable VLSI chip that
you program yourself to perform the functions you need. It operates
at logic speed, not at processor speed.


Thanks. I'll look into it. I suspect my abilities might be constrained to
running my code as currently, on a PC with at least 1 GHz for the 48+ voice
polyphony I'm getting, but Yamaha hadn't got that when they got 16 voices out
of a DX7 so I do at least have a strong incentive to explore.