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Re: AUDITORY Digest - 19 Nov 2011 to 20 Nov 2011 (#2011-271)
One more note to add about the TDT PA5 --- this device tends to
produce a transient when the attenuation level is switched, which
therefore can produce a click. To correct this problem it is
necessary to use a lowpass filter on the output, e.g. with corner
frequency 100 or 120kHz, and for neural recording it would also be
advisable to design stimuli such that the attenuation change is
separated in time from the onset of the intended auditory stimuli.
> Date: Sun, 20 Nov 2011 20:26:51 -0500
> From: =?ISO-8859-2?Q?Pawe=B3_Ku=B6mierek?= <pawel.kusmierek@xxxxxxxxx>
> Subject: attenuator - response summary
> Content-Type: text/plain; charset=ISO-8859-1
> Hello everyone,
> thanks to everyone who replied to my question about attenuators.
> Some responses were off-list, and some were "off-off-list" (I asked
> elsewhere), so here is the summary.
> To remind you, I was looking for a "commercially available precise
> digitally controlled (i.e., repeatable) attenuator with fast and quiet
> attenuation changing. Preferably, but not necessarily controlled via RS232."
> The RS232 was suggested because I want it to be controlled from CED
> Spike2/Power1401 system or from NBS Presentation, or from similar systems,
> and RS232 looked like a sensible (although pretty old) solution.
> Basically there were two suggestions.
> 1. TDT PA2
> - wide attenuation range of ~120 dB (0 to - 120dB),
> - small gain step (0.1 dB),
> - high accuracy (0.05 dB),
> - good noise/distortion figures
> - manual control possible
> - attenuation value is displayed
> - ready to use
> - price: $725 for a single channel device, but additional control/power/PCI
> cards, etc. hardware and software are needed, which drives the price of a
> single-channel attenuator to ~$2,500. I think that the second channel can
> be added for additional $725 only, but still it is not cheap
> - control: via an AciveX control, I am not exactly sure if (and how) I
> could do this from CED or NBS systems.
> A person suggested TDT RX5 and I was not able to find what it is. However,
> RX6 and RX7 appear to be powerful DSP devices, so RX5 is probably too much
> capability-wise and price-wise than I need. Please correct me if I am wrong
> 2. A "digital potentiometer" chip. Specific models suggested were Dallas
> Semiconductors DS1801, Cirrus CS3310 (or 3308 for 8 channels) and Texas
> Instruments PGA2320.
> - low price - the chip itself is in $5-$20 range, for a 2-channel device
> - wide attenuation range ~127 dB for the CS and PGA (~63 dB for the DS)
> - pretty small gain step/accuracy (CS: 0.5/0.05 dB, PGA 0.5/0.1 dB, DS
> 1/not sure)
> - good noise/distortion figures
> - control via three serial TTL lines (more may be needed if certain
> features cannot be set to enabled or disabled permanently) - this could be
> achieved from NBS Presentation via LPT printer port or NI I/O board, and
> from CED Spike2 via the 1401 interface
> - zero-crossing mode - the chips may be set to attempt to change
> atttenuation on analog zero-crossing to reduce artifacts
> - a device has to be built around the chip - power supply (PGA: +5V, +15V,
> -15V, CS: +/- 5V, DS: +3 or + 5V), connectors, possibly buffers. This will
> increase the total price, but definitely it will be still well below TDT
> PA5 price, even with labor factored in.
> - for CS and PGA the 127-dB attenuation range is NOT 0 to -127dB, it is
> +31.5dB to - 95.5dB, which may have clipping implications
> - no manual control and no way to read back the set value (unless special
> steps are taken)
> One person warned me that "digtal audio attenuators" typically do not have
> 1 dB steps, but fine steps at high levels and coarser steps at lowe levels.
> However, the chips that were suggested to me have 0.5 or 1 dB steps over
> their attenuation range.
> He also proposed using and old SoundBlaster SB16 or AWE32 as an attenuator.
> These cards need a computer with ISA bus, which are not available for me
> (and frankly, I doubt there are many operational machines from these days
> Thanks again to everyone for your suggestions,
Jennifer F. Linden, Ph.D.
Lecturer in Neuroscience
UCL Ear Institute
and Dept. of Neuroscience, Physiology & Pharmacology
332 Gray's Inn Road
London, WC1X 8EE
Tel: +44 (0)20 7679 8928 (internal x28928)
Fax: +44 (0)20 7837 9279