[sdiy] Cheap audio spectrum analyzer.. finally..

rsdio at audiobanshee.com rsdio at audiobanshee.com
Wed Oct 28 20:05:11 CET 2015

Almost. But not quite.

Glissando is a chromatic series.

The non-"chirp" signal used to prime an FFT is a harmonic series.

Now, where're the synth module with a switch to create a harmonic slide instead of glissando or portamento? Wouldn't that be cool?… (but difficult to pull off when the starting and ending notes are not both part of the same harmonic series).


On Oct 28, 2015, at 1:23 AM, Roman Sowa <modular at go2.pl> wrote:
> That's called glissando
> :)
> Roman
> W dniu 2015-10-28 o 08:28, rsdio at audiobanshee.com pisze:
>> Thanks for the info.
>> There must be a different term for a "chirp" that only contains
>> frequencies of integral multiples of the sample rate, because the
>> standard definition of chirp is a sweep over a continuous range of
>> frequencies. The latter kind even occur naturally in audio-frequency
>> radio waves.
>> Brian
>> On Oct 27, 2015, at 10:25 PM, Tim Ressel <timr at circuitabbey.com> wrote:
>>> Quite sure. The chirp was generated using an inverse FFT. This
>>> ensures there is energy only in the FFT buckets, thus preventing
>>> the spill over you usually get with FFTs.
>>> On 10/27/2015 9:51 PM, rsdio at audiobanshee.com wrote:
>>>> Are you sure it's using an FFT in that mode? As the videos show,
>>>> it's possible to do the whole process in the time domain. If the
>>>> scope has a rectifier mode, you'd get a clean line instead of a
>>>> solid shape for the envelope.
>>>> Brian
>>>> On Oct 27, 2015, at 12:10 PM, Tim Ressel <timr at circuitabbey.com> wrote:
>>>>> I have used the 35660 extensively. It is an excellent box for
>>>>> its age. It has a mode where you feed a chirp through the DUT
>>>>> and it magically smooths out the FFT results and gives a clean
>>>>> line. Very nice!  Wish I had one.

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