I use pink noise for all my tests that involve a signal like speech. I agree
Jim that it is the proper signal character for the mode.
73
Bob, K4TAX
Sent from my iPhone
> On Jul 28, 2014, at 11:56 AM, Jim Brown <k9yc@audiosystemsgroup.com> wrote:
>
>> On 7/28/2014 9:36 AM, Kim Elmore wrote:
>> I've been thinking, too. A square wave has an infinite number I'd odd
>> harmonics, not all harmonics. Regardless, it's an excellent way to look at
>> IMD, far better than two tones.
>
> Yup.
>>
>> What if we modulated the TX with pink noise? That really does have
>> everything in it. Make the pink noise much wider than the expected audio
>> bandwidth. Ideally, the spectrum should be limited to the TX filtered BW.
>> Wouldn't this be nearly the most severe test?
>
> Actually, it's a near ideal test for performance of the rig on SSB. One of
> the major virtues of pink noise as a test signal is that it roughly
> approximates the spectrum of both music and speech. In pro audio, we've used
> "shaped" pink noise for years to specify the performance of loudspeakers,
> where the shaping is simply bandpass filtering of pink noise for the region
> where the loudspeakers are intended to operate. I strongly encourage the use
> of pink noise shaped to a bandwidth of 100 Hz to 5 kHz for this purpose.
>
> I've discussed this with Rob Sherwood several times, and taken him to task
> for using white noise for that purpose because it does NOT approximate
> speech. His response is that his intent is to represent clipped and distorted
> audio. My problem with that is that good audio signal processing should be
> tailored to the spectra of speech, so using white noise as a test signal will
> cause that signal processing to misbehave (or behave differently from how it
> would work with speech).
>
> For those who don't know, pink noise is random noise with equal power per
> PERCENTAGE bandwidth -- per octave, per third-octave, per sixth-octave, etc.
> It can be generated by applying a 3dB/octave rolloff to white noise.
>
> 73, Jim K9YC
>
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