germanium
Headphoneus Supremus
Note this applies to all sources computer or otherwise.
Main type of DAC's
1. The original which is ladder type DAC's
These have a resister network of precision resisters for one for each bit level each representing 6db increase in output. early versions were 14-16 bit as available to consumers. These early DAC's had no digital filter & were filtered externally by an analog filter.
Advantage of this design was they were simple to design & when properly set up had very good sound though not necessarily great.
Later designs of these DAC's externally had a digital filter feeding them. Higher end versions of these DAC's sounded great when properly designed. It was about this time that 18-20 bit high precision chip DAC's also started to appear in which the resister networks were laser trimmed for extreme accuracy which did indeed contribute to their excellent sound. Earlier versions had quite gross errors in some cases where the laser trimming fixed this.
Disadvantages were that these DAC's were extremely prone to input jitter as well as gross nonlinear distortions in the lower end DAC chips.
Later versions of these DAC's moved the digital filter onto the DAC chip itself.
2.Delta-sigma I.E. 1 bit DAC's.
These DAC's were in some ways easier to design but in other ways more difficult.
These DAC's traded absolute amplitude linearity for time based amplitude linearity.
These got rid of the resistor ladder & used pulse density in order to achieve amplitude linearity. This is essentially the same as DSD used in SACD.
Advantages with this DAC type was that low level linearity was vastly improved in the lower price ranges. There were also less prone to input jitter due to sample rate conversion from low sample rates such as4 4.1 KHz up to as high 100MHz in current DAC's as as opposed to clock jitter. These pretty much all have internal digital filters.
Disadvantages were that They were more prone to clock jitter as the linearity is achieved through pulse density if those pulses were ill timed it could result in nonlinear behavior to a greater extent than ladder type converters since the ladder types linearity was not based on the clock but on the precision of it's ladder resistors. The higher the clock speed by the way the more important the clock jitter can be as an equally small deviation such as 100 picoseconds in clock represents a larger proportion in time shift at higher clock speeds.
3. Hybrid delta-sigma DAC's
Many complained that the pure delta-sigma DAC's did not seem to represent the full dynamics of the program material as well as the higher end ladder DAC's. To counter this the designers created hybrid delta-sigma DAC's that had 6 bits instead of only a single bit. These DAC's the lower levels were still represented by a single bit. From -24db upwards the signal was represented by a 6 bit ladder portion supposedly giving better high level dynamics which was to address the complaints of the loss of dynamics in the original delta-sigma DAC's. Most DAC's currently are of this design.
Advantage is that these DAC's have seemed at least to address the earlier complaints of pure delta-sigma DAC's
Disadvantage is that they are more costly to buy than pure delta-sigma DAC's but cheaper than high end ladder DAC's.
4. Field programmable gate array DAC's
These DAC's are basically micro computers that are being utilized as DAC's. They most likely are using the hybrid delta-sigma type of conversion & using much of the power for their digital filter configuration as well as some correction for distortion in the following analog stages.
Advantage is the manufacturer can easily upgrade the software for the DAC without the end user having to bring it in the DAC for servicing as there is no need to change any hardware. Changes in programing for the DAC could include better corrections for analog stage distorting & offering different digital filter types which they feel may improve the sound.
Disadvantage is that these DAC chips are extremely expensive as well as being very power hungry compared to other types of DAC's. These higher power draws can introduce higher levels of noise in the power supply. Most modern opamps deal pretty well with this though. Chord for example does the actual conversion to analog off chip using external array of flip-flops supposedly minimizing EMI crosstalk by physically separating these components.
A note on sample rate conversion
Almost all current DAC's do sample rate conversion of some type. Sample rate conversion when done properly can reduce or eliminate sensitivity to input jitter as being a factor in the sound quality of the DAC. The most robust of these is asynchronous sample rate conversion as the output no longer bears any timing relationship to the input sample rate.
Sample rate conversion has been proven to be transparent when properly done & can be converted back to the original sample rate with absolute zero loss proven by null testing.
Too many people think they are gaining something by not allowing sample rate conversion. Even if you prevent sample rate conversion leading up to the DAC most DAC's still convert sample rate internally. Most of them to an exact multiple but some do it to a multiple that is completely unrelated such as ESS Sabre DAC's. If done properly this is the most robust input jitter elimination technique.
Main type of DAC's
1. The original which is ladder type DAC's
These have a resister network of precision resisters for one for each bit level each representing 6db increase in output. early versions were 14-16 bit as available to consumers. These early DAC's had no digital filter & were filtered externally by an analog filter.
Advantage of this design was they were simple to design & when properly set up had very good sound though not necessarily great.
Later designs of these DAC's externally had a digital filter feeding them. Higher end versions of these DAC's sounded great when properly designed. It was about this time that 18-20 bit high precision chip DAC's also started to appear in which the resister networks were laser trimmed for extreme accuracy which did indeed contribute to their excellent sound. Earlier versions had quite gross errors in some cases where the laser trimming fixed this.
Disadvantages were that these DAC's were extremely prone to input jitter as well as gross nonlinear distortions in the lower end DAC chips.
Later versions of these DAC's moved the digital filter onto the DAC chip itself.
2.Delta-sigma I.E. 1 bit DAC's.
These DAC's were in some ways easier to design but in other ways more difficult.
These DAC's traded absolute amplitude linearity for time based amplitude linearity.
These got rid of the resistor ladder & used pulse density in order to achieve amplitude linearity. This is essentially the same as DSD used in SACD.
Advantages with this DAC type was that low level linearity was vastly improved in the lower price ranges. There were also less prone to input jitter due to sample rate conversion from low sample rates such as4 4.1 KHz up to as high 100MHz in current DAC's as as opposed to clock jitter. These pretty much all have internal digital filters.
Disadvantages were that They were more prone to clock jitter as the linearity is achieved through pulse density if those pulses were ill timed it could result in nonlinear behavior to a greater extent than ladder type converters since the ladder types linearity was not based on the clock but on the precision of it's ladder resistors. The higher the clock speed by the way the more important the clock jitter can be as an equally small deviation such as 100 picoseconds in clock represents a larger proportion in time shift at higher clock speeds.
3. Hybrid delta-sigma DAC's
Many complained that the pure delta-sigma DAC's did not seem to represent the full dynamics of the program material as well as the higher end ladder DAC's. To counter this the designers created hybrid delta-sigma DAC's that had 6 bits instead of only a single bit. These DAC's the lower levels were still represented by a single bit. From -24db upwards the signal was represented by a 6 bit ladder portion supposedly giving better high level dynamics which was to address the complaints of the loss of dynamics in the original delta-sigma DAC's. Most DAC's currently are of this design.
Advantage is that these DAC's have seemed at least to address the earlier complaints of pure delta-sigma DAC's
Disadvantage is that they are more costly to buy than pure delta-sigma DAC's but cheaper than high end ladder DAC's.
4. Field programmable gate array DAC's
These DAC's are basically micro computers that are being utilized as DAC's. They most likely are using the hybrid delta-sigma type of conversion & using much of the power for their digital filter configuration as well as some correction for distortion in the following analog stages.
Advantage is the manufacturer can easily upgrade the software for the DAC without the end user having to bring it in the DAC for servicing as there is no need to change any hardware. Changes in programing for the DAC could include better corrections for analog stage distorting & offering different digital filter types which they feel may improve the sound.
Disadvantage is that these DAC chips are extremely expensive as well as being very power hungry compared to other types of DAC's. These higher power draws can introduce higher levels of noise in the power supply. Most modern opamps deal pretty well with this though. Chord for example does the actual conversion to analog off chip using external array of flip-flops supposedly minimizing EMI crosstalk by physically separating these components.
A note on sample rate conversion
Almost all current DAC's do sample rate conversion of some type. Sample rate conversion when done properly can reduce or eliminate sensitivity to input jitter as being a factor in the sound quality of the DAC. The most robust of these is asynchronous sample rate conversion as the output no longer bears any timing relationship to the input sample rate.
Sample rate conversion has been proven to be transparent when properly done & can be converted back to the original sample rate with absolute zero loss proven by null testing.
Too many people think they are gaining something by not allowing sample rate conversion. Even if you prevent sample rate conversion leading up to the DAC most DAC's still convert sample rate internally. Most of them to an exact multiple but some do it to a multiple that is completely unrelated such as ESS Sabre DAC's. If done properly this is the most robust input jitter elimination technique.
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