[sdiy] uLaw DACs in the modern era?

[rsdio at audiobanshee.com]

Seconded.

I was going to suggest a straight 16-bit DAC. I mean, you can get 8-bit quality with a 16-bit DAC just by left-justifying the samples (provided that you account for any unsigned versus signed differences). There’s no reason why you can’t get 12-bit, 13-bit, or the strange variable quantization of u-Law or A-law.

The original reasons for 8-bit and u-Law were the memory limitations and expense of precision DAC chips at the time. These days, memory and precision are not a challenge. So, if you still want the grunginess of variable quantization, just bake it into the samples.

You probably want to do your sample processing offline, though, unless you want to double sample memory at the expense of other signal processing power.

Brian


On May 19, 2018, at 12:21 PM, paula at synth.net wrote:
> Tom,
> 
> Why go for a hard to find DAC? why not recreate it?
> 
> I "recreated" the uLaw using a 12 bit DAC and an 8 bit LUT. Then I was able to play back the LInn samples directly.. sounded pretty nice too IMHO. Ok, yes I should've used 13bits, but I didn't have any 14bit DACs to hand, but I did have 12 bit, so I went with that.
> 
> Paula
> 
> On 2018-05-19 11:08, Tom Wiltshire wrote:
>> Hi All,
>> Over the last couple of days I’ve been studying early drum machines,
>> mostly the Linn LM-1 and the Oberheim DMX.
>> Both of these machines use 8-bit memory, but manage a 12-bit dynamic
>> range by using a u-Law coding and outputting samples via the AM6070
>> u-Law DAC. Datasheet here if you’re interested:
>> http://synfo.nl/datasheets/AM6070.pdf
>> Does anything like this exist any longer? It seems to me that the
>> unusual DAC response is big part of the “thump” of these early
>> machines, since it has considerable distortion, but manages to spread
>> it to areas where it’s perceptually less noticeable (so higher level
>> signals have less detail than lower level signals).
>> Alternatively, would it be possible to build such a device? The
>> combination of a 4-bit value plus some gains and offsets doesn’t seem
>> impossible to manage, but I’d be interested to hear people’s ideas for
>> how you’d do it.
>> Thanks,
>> Tom
>> ==================
>>       Electric Druid
>> Synth & Stompbox DIY
>> ==================