[sdiy] large numbers

[Tom Wiltshire]

Ha, Richie beat me to it! Yes, exactly!

> On 13 Jul 2018, at 21:21, Richie Burnett <rburnett at richieburnett.co.uk> wrote:
> 
> More bits in the phase accumulator doesn't reduce the jitter, it just increases the resolution with which you can set the average output frequency. The absolute jitter is determined by the reciprocal of the sample rate.
> 
> It is increasing the sample rate relative to the frequency that the Nco is generating, that decreases the relative jitter in the nco's raw phase accumulator output, and makes it sound better. 
> 
> If you used a sample rate of a few hundred MHz then a raw Nco output will sound completely alias-free over the entire audio range, and you don't need anywhere near 64bit word length. With 200 Mhz sample rate, a 32 bit phase accumulator lets you set the output frequency to 0.047 Hz resolution!
> 
> For a pitch look up table you don't even need anywhere near 32-bit resolution. Just store one octave's worth of pitch values left-justified in 16-bit integers and then shift the value right accordingly into a larger phase-increment register to produce notes with successively lower octaves.
> 
> -Richie, 
> 
> Sent from my Xperia SP on O2
> 
> ---- Tim Ressel wrote ----
> 
>> If you must pry...  ;-)
>> 
>> I am playing with using a 64 bit accumulator in a DCO (NCO?) to fix the 
>> top jitter problem. The notion is that increased resolution in the 
>> increment value will cause less top jitter.
>> 
>> --tr
>> 
>> 
>> On 7/13/2018 11:30 AM, Richie Burnett wrote:
>>> Out of interest, what application requires table lookup of values to a resolution of better than 1 part in 10 to the 19 !?!?!?
>>> 
>>> -Richie,
>>> 
>>> Sent from my Xperia SP on O2
>>> 
>>> ---- Tim Ressel wrote ----
>>> 
>>>> Verified. I don't relish (or other condiment...) doing that calc
>>>> manually 4096 times. But it does tell us that a windoze machine can do
>>>> the deed. I wonder if its a matter of floats versus doubles?
>>>> 
>>>> --timmers
>>>> 
>>>> 
>>>> On 7/13/2018 9:59 AM, Ben Bradley wrote:
>>>>> Windows Calculator does about twice that ("In Scientific mode,
>>>>> Calculator is precise to 32 significant digits."), though of course
>>>>> using it is tedious. If it helps, you can copy-paste operations into
>>>>> it. Copy and paste this:
>>>>> 2y2r=
>>>>> (two to the power of 2 reciprocal - this calculates the square root of
>>>>> two) gives:
>>>>> 1.4142135623730950488016887242097
>>>>> There's a list of keyboard shortcuts somewhere.
>>>>> 
>>>>> If you're using integers, I recall that Python, rather than
>>>>> overflowing, will handle arbitrarily large integer values.
>>>>> 
>>>>> 
>>>>> On Fri, Jul 13, 2018 at 12:42 PM, Tim Ressel <timr at circuitabbey.com> wrote:
>>>>>> Hey'all,
>>>>>> 
>>>>>> I need to generate a lookup table with 64 bit values. Usually I use Excel
>>>>>> but there is a problem: It only does 14 decimal places. I don't think this
>>>>>> is enough. Any suggestions?
>>>>>> 
>>>>>> --
>>>>>> --Tim Ressel
>>>>>> Circuit Abbey
>>>>>> timr at circuitabbey.com
>>>>>> 
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>>>> -- 
>>>> --Tim Ressel
>>>> Circuit Abbey
>>>> timr at circuitabbey.com
>>>> 
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>> 
>> -- 
>> --Tim Ressel
>> Circuit Abbey
>> timr at circuitabbey.com
>> 
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