Re: Clip-level question
Re: Clip-level question
- Subject: Re: Clip-level question
- From: Brian Willoughby <email@hidden>
- Date: Tue, 3 Jun 2008 18:05:38 -0700
I'm not sure what you're doing, or what you're asking, Glenn, but +30
dB would correspond to approximately +/- 31.6 floats. How have you
determined that +30 dB gain is not clipping?
We've covered this before, but +/- 1.0 floats would actually clip on
the positive side. The -1.0 value can be converted to a precise
value by the DAC, but the +1.0 value would be clipped to the next
smaller 24-bit value (or 16-bit value, as appropriate). Your -1 dBFS
is more than sufficient to avoid clipping due to this fact of two-
complement DAC coding. In fact, anything below -0.00026507638 dBFS
would be safe for any digital output that is at least 16 bits.
-0.03399569756 dB would protect even 8-bit DACs from clipping on the
positive side, but who uses 8-bit these days, even in video games?
If you create your samples at -1 dBFS correctly, then you should not
be able to apply any gain over 1.0 without clipping. I suspect that
your samples or your float conversion is not working as you suspect,
or I have misread your description. Are you applying a gain of less
than 1.0?
As far as I know, the maximum setting of system volume will not clip
a signal that stays below 0 dBFS. I'm not sure what you're asking in
your final question, but 0 dBFS corresponds to maximum system volume
without clipping - at not clipping in the digital domain. However,
the analog circuitry in some Macs will clip with certain content, so
you might have to back off on the system volume a few steps. Using
professional audio interfaces should allow you to avoid analog
clipping at maximum system volume, and perhaps even the headphone
output might be cleaner than the built-in speakers, if you ignore the
noise.
If this doesn't answer your questions, we might need a few more
details of your setup, including how you are confirming your results.
Brian Willoughby
Sound Consulting
On Jun 3, 2008, at 15:41, Glenn Zelniker wrote:
Sorry if this has been asked before, but I can't seem to find a
satisfactory answer.
I am trying to determine the level at which a sine wave will produce
audible clipping. To wit, I am playing a sine wave (1 kHz @ -1 dBFS)
from disk using a small test program I wrote. I convert these samples
to floats and apply gain before sending the samples off to the
output. I've found that depending on the position of the system
volume-control, the amount of gain I can apply varies before clipping
occurs. This would seem to indicate that the system volume-control is
operating pre-DAC, no? But I've yet to find any kind of calibration
information that explains the peak level that a sine wave can achieve
without resulting in clipping, as a function of the position of the
system volume-control. With the system volume set to maximum, it
appears that I can send out values larger than 30 dB above what I
would have thought was full scale (relative to +/- 1.0 floats).
So, can anyone tell me what the peak sine clip level is as a function
of the system volume control?
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