[sdiy] tempco puzzle

[Chris Stecker]

On Tuesday 01 October 2002 01:18 pm, Andre Majorel wrote:
> On 2002-10-01 15:27 +0100, Seb Francis wrote:
> > What would you say the target "smallest noticeable difference"
> > would be for a perceptive human?  Paul Perry suggested 1dB, but
> > does this also depend on the actual volume?
>
> It somewhat depends on volume and frequency (see the
> Fletcher-Munson curves). I don't known the exact figures but an
> error of 1 dB over 10°C seems quite acceptable in a synth
> application. Errors could cause trouble if the output level is
> not just a matter of loudness (E.G. the VCA output is used for
> linear FM), or if the error causes clipping.

Just-noticable-differences (JNDs) for wideband noise are in the range 0.5-1 
dB, pretty constant across levels. For tones, JNDs decrease at higher levels. 
At 1000 Hz, figure 1.5 dB at 20 dB above threshold, 0.3 dB at 80 dB.  JNDs 
are somewhat smaller at high frequencies than low frequencies.  (Data 
reported in B. C. J. Moore, "An introduction to the psychology of hearing," 
3rd Ed.) These are all for direct comparisons in a laboratory setting, 
however, and don't imply that even a careful listener could identify a sound 
as being 1 dB away from spec. I'd say 1 dB is probably good enough.  

-Chris



-- 

G. Christopher Stecker, Ph.D.                                              
cstecker at umich.edu       /    734-764-5167

Central Systems Laboratory, Kresge Hearing Research Institute                 

University of Michigan Medical Center
1301 East Ann Street / Ann Arbor MI 48109-0506