[time-nuts] Misuse of word "decimate" (was Re: Short term 10MHz source)

[Magnus Danielson]

Peter,

No, it's not truncation per se.

Let's say you have 100 samples. With a 10-to-1 decimation you reduce 
them into 10 samples in whatever method maintaining the core value 
(phase for instance). As you do that, you get more and more bits as 
these is combined. For larger decimation ratios (often hierarchially) 
you end up having so many bits that eventually you also truncate the 
lower parts, but that is something you would try to avoid when you can.

I hope that clarifies it for you.

I am in a meeting now, so that is why I am brief.

Cheers,
Magnus - at IFCS2019 JTPC working for Group 2

On 2019-01-10 14:12, Peter Vince wrote:
> Thank you for your reply Magnus.  Could you please clarify then exactly
> what "decimate" means in this context.  Is it "truncation", i.e.
> eliminating or ignoring the last few digits, be they decimal or binary?
> And/or is there some rounding involved?
>
>       Peter
>
>
> On Thu, 10 Jan 2019 at 13:01, Magnus Danielson <magnus at rubidium.se> wrote:
>
>> Peter,
>>
>> While the word derives back to the Roman times, today it is a technical
>> term for data-reduction being used in professional literature, so it's
>> meaning has already been established.
>>
>> For instance, in modern phase-noise measurement setups the sample-rate
>> is around 100 MS/s, and that sample-rate of multiple ADCs with
>> relatively high amounts of bits is way to high to hand over to software,
>> so it is decimated down in steps in FPGA before handing over to
>> software. Decimation is the term used in that context.
>>
>> Cheers,
>> Magnus
>>
>> On 2019-01-10 13:01, Peter Vince wrote:
>>> In his comment below, Mark has used the word "decimate".  There is much
>>> debate about what this word means (presently, and/or in the past), but
>>> common explanations refer back to Roman times when they apparently killed
>>> one person in ten as a punishment, and similarly "tithes" - or taxes,
>> where
>>> one in ten was taken.  Now OK, you can argue this until the cows come
>> home,
>>> but the result is that the meaning isn't crystal clear, and particularly
>> on
>>> a technical forum where precision is paramount, and the entire reason we
>>> are here, I believe accuracy and clarity of expression is also important.
>>> In this instance, I believe "truncate" would be a better word.
>>>
>>> </rant>  :-)
>>>
>>>        Regards,
>>>
>>>             Peter Vince
>>>
>>> On Wed, 9 Jan 2019 at 23:56, Mark Sims <holrum at hotmail.com> wrote:
>>>> ...
>>>> And as far as decimating the TICC output values in firmware... please
>>> don't.   Let the user decimate the values if they want to.
>>
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