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Pseudo-random questions about a professional audio application

Started by Shaun August 16, 2003
Hello all,

I've been toying with the idea of putting together a DSP
box with some audio I/Os and am looking to get the highest
quality audio fed into my DSP as possible.  The engineering
side of me wants to start by getting the skinny on 'the best'
sampling techniques, ADCs, and pre-DSP stages to minimize (or
ideally eliminate) quantization noise.  However, the business
side of me says I should begin prototyping the software on
some cheap COTS embedded system with the lowest-noise path
to the same DSP/s, DSP library, CPU, RTOS, etc., etc. as I'd
like inside the final system.  The engineering side, without
regard for cost whatsoever, would probably want an entirely
custom board made before he began any work anyways ;-).

That said, does anyone have any recommendations about embedded
boxes which come ready for prototyping audio applications?  How's
the price on one of these things anyways?  Is there the slightest
chance in heck I can find a high-end COTS board with multiple 1/4
inch TRS (tip-ring-sleeve) I/Os and a minimum quantization noise
path to a cool fixed-point 16/24/32-bit DSP/s?  MIDI support and
IDE/SCSI would be cool too!  Additional ideas on where to look
would be great to hear about.

On the engineering side, is delta-sigma modulation the best appro-
ach for reducing sampling errors or are there other techniques which
work better for signals in the less-than 50kHz range?  Does its qual-
ity stem from the fact that the quantization noise is pushed beyond
the frequency range of interest where it can be easily LP-filtered out?
Also, I'm told the ADCs which use it are a bit more expensive than
traditional sample-and-hold ADCs.  Are the differences in cost managable
for low-yield production?

Thanks very much in advance!

Cheers,
Shaun
elvis_costello79@yahoo.com (Shaun) wrote in 
news:f9bb5092.0308152229.3eac43eb@posting.google.com:

> Hello all, > > I've been toying with the idea of putting together a DSP > box with some audio I/Os and am looking to get the highest > quality audio fed into my DSP as possible. The engineering > side of me wants to start by getting the skinny on 'the best' > sampling techniques, ADCs, and pre-DSP stages to minimize (or > ideally eliminate) quantization noise. However, the business > side of me says I should begin prototyping the software on > some cheap COTS embedded system with the lowest-noise path > to the same DSP/s, DSP library, CPU, RTOS, etc., etc. as I'd > like inside the final system. The engineering side, without > regard for cost whatsoever, would probably want an entirely > custom board made before he began any work anyways ;-). > > That said, does anyone have any recommendations about embedded > boxes which come ready for prototyping audio applications? How's > the price on one of these things anyways? Is there the slightest > chance in heck I can find a high-end COTS board with multiple 1/4 > inch TRS (tip-ring-sleeve) I/Os and a minimum quantization noise > path to a cool fixed-point 16/24/32-bit DSP/s? MIDI support and > IDE/SCSI would be cool too! Additional ideas on where to look > would be great to hear about. > > On the engineering side, is delta-sigma modulation the best appro- > ach for reducing sampling errors or are there other techniques which > work better for signals in the less-than 50kHz range? Does its qual- > ity stem from the fact that the quantization noise is pushed beyond > the frequency range of interest where it can be easily LP-filtered out? > Also, I'm told the ADCs which use it are a bit more expensive than > traditional sample-and-hold ADCs. Are the differences in cost
managable
> for low-yield production? > > Thanks very much in advance! > > Cheers, > Shaun >
Most of the newest state of the art converters are sigma delta. Perhaps, the biggest advantage of these converters is that you don't need to use high order antialiasing filters or antiimaging filters. We have a few products that you might be interested in. We have our dspstak 21161 Sharc based DSP board and next week we will be officially announcing our dspstak 21262 board. The ADSP-21262 was just announced by ADI last Monday. We have been working with ADI for some time with this chip. Dspstaks use two pc assemblies. We divide the I/O functions from the DSP Engine since the I/O is the most custom part of many systems. We are working on several new I/O modules. WE might have a suitable I/O module for your needs or if you can define your needs well enough and we think there is a market, we will problably create a new one. One of the big advantages of separating the I/O from the DSP is that new I/O modules are very easy to create since there is not really that much circuitry required. The biggest challenge is often picking suitable connectors. -- Al Clark Danville Signal Processing, Inc. -------------------------------------------------------------------- Purveyors of Fine DSP Hardware and other Cool Stuff Available at http://www.danvillesignal.com
"Shaun" <elvis_costello79@yahoo.com> wrote in message
news:f9bb5092.0308152229.3eac43eb@posting.google.com...
> Hello all, > > I've been toying with the idea of putting together a DSP > box with some audio I/Os and am looking to get the highest > quality audio fed into my DSP as possible. The engineering > side of me wants to start by getting the skinny on 'the best' > sampling techniques, ADCs, and pre-DSP stages to minimize (or > ideally eliminate) quantization noise. However, the business > side of me says I should begin prototyping the software on > some cheap COTS embedded system with the lowest-noise path > to the same DSP/s, DSP library, CPU, RTOS, etc., etc. as I'd > like inside the final system. The engineering side, without > regard for cost whatsoever, would probably want an entirely > custom board made before he began any work anyways ;-). > > That said, does anyone have any recommendations about embedded > boxes which come ready for prototyping audio applications? How's > the price on one of these things anyways? Is there the slightest > chance in heck I can find a high-end COTS board with multiple 1/4 > inch TRS (tip-ring-sleeve) I/Os and a minimum quantization noise > path to a cool fixed-point 16/24/32-bit DSP/s? MIDI support and > IDE/SCSI would be cool too! Additional ideas on where to look > would be great to hear about.
The very best audio quality will probably be obtained by using a DSP board that has digital inputs (e.g. AES/EBU) and external ADCs/DACs. There are lots of good pro-audio ADC boxes out there that will give you 110dB or more dynamic range. One example would be: http://www.lucidaudio.com/products/product_ad_9624_info.htm I don't know of any DSP development platforms that have digital audio connections, but there may be some out there. That said, very good performance can still be obtained with the converters in the same box as the DSP stuff if good design practices are used. You will have to decide on the specifications requried by your application to see which approach is most appropriate.
> On the engineering side, is delta-sigma modulation the best appro- > ach for reducing sampling errors or are there other techniques which > work better for signals in the less-than 50kHz range? Does its qual- > ity stem from the fact that the quantization noise is pushed beyond > the frequency range of interest where it can be easily LP-filtered out? > Also, I'm told the ADCs which use it are a bit more expensive than > traditional sample-and-hold ADCs. Are the differences in cost managable > for low-yield production?
Check out the converter IC offerings by AKM and Crystal/Cirrus and others. The data sheets should tell you all you need to know.