Sound Devices 664 OP timing

[Bash]

I was driving along ths morning, and my mind was wandering, and after some confusion, I ended up asking a question to which I had no idea of the answer....

So - SD664 is a 6 IP, into 4 buss analogue mixer with a digital recorder that can sniff both the IP tracks and the mix busses.

I was wondering at what point do things get A to D'd, and are there any implications here with OP timing?

So - my question is really to do with the time domain of the OPs - are the direct out analogue OPs in time with the main analogue OPs, and are the Aux analogue OPs in time with the main analogue OPs?

This then raises another question, which is a similar thought to do with AES42 digital mic IPs, when mixed with analogue IPs. If I have a digital mic plugged into one IP channel (I think it is channels 1 and 6 that can take AES 42 mics), and an analogue mic plugged into IP channel 2... will they arrive onto say the main mix bus in the same time domain?

Kindest regards,

Simon B aka intrigued of Ealing....

[pindrop]

Good questions, you can delay all the analog inputs to match the digital mic input on the 788T for example but I've not seen any mention of user selectable delay on the 664?

[Matt Mayer]

Simon,

From the FAQ up on the 664 page:

Q: Are signals summed in analog, like the rest of the mixer line, or digital, like the 7-Series?

A: The 664 offers both analog and digital summing. The input-to-mix and mix-to-analog outputs are all-analog signal paths. This provides for superb sonic performance. Top music engineers often use analog summing mixers for their sonic benefits versus "in the box" digital mixing.

Q: What happens with digital mics? Is their signal going through the mixer in analog or digital?

A: Either! AES42 inputs go through high-resolution sampling rate converters and are sent digitally to the DSP. When that signal is routed to a record track or to an AES output, it remains in digital. Signals in the DSP sent to analog outputs run through a DAC (digital-to-analog converter).

AFAIK, there is no delay on the analog inputs.

[Jeff Wexler]

Simon,

From the FAQ up on the 664 page:

Q: Are signals summed in analog, like the rest of the mixer line, or digital, like the 7-Series?

A: The 664 offers both analog and digital summing. The input-to-mix and mix-to-analog outputs are all-analog signal paths. This provides for superb sonic performance. Top music engineers often use analog summing mixers for their sonic benefits versus "in the box" digital mixing.

Q: What happens with digital mics? Is their signal going through the mixer in analog or digital?

A: Either! AES42 inputs go through high-resolution sampling rate converters and are sent digitally to the DSP. When that signal is routed to a record track or to an AES output, it remains in digital. Signals in the DSP sent to analog outputs run through a DAC (digital-to-analog converter).

AFAIK, there is no delay on the analog inputs.

It was a good question but now I am confused by the answer. If you are utilizing both analog signals at the inputs and AES digital signals at their inputs, how can the timing at the output be correct? If you are using both analog summing and digital summing, how does that work? I'm not so well versed in these things (since I am such an old school analog person) and I do understand how this all works when it is strictly digital mixing in the box, just curious with this method of analog summing and digital summing.

[John Blankenship]

It appears that the analog mics need to be placed a proper distance away from the sound source to match the delay of the digital mics <g>.

[Eric Toline]

..or you could just add 500' of mic cable to the analog mics to get the same delay.

Eric

[John Blankenship]

..or you could just add 500' of mic cable to the analog mics to get the same delay.

Those are some slow electrons you're using, Eric. (Or, should I say, "slow holes" depending upon your electronic religion.)

[pindrop]

It appears that the analog mics need to be placed a proper distance away from the sound source to match the delay of the digital mics <g>.

So which manufacturer can come up with a user selectable in line delay cable first? Could it be powered by phantom power and just be a slug like the phantom powering mic cables for transmitters, and have a little screwdriver pot in it to select ms delay? Is this possible?

Otherwise it's 500' of cable, or the mic 65'+ feet from the source which isn't going to get me repeat work enquiries so much......

[Matt Mayer]

Simon,

Sorry, didn't read all the way through your question. Need to have my coffee before posting....

For all analog inputs, the path is completely analog inputs to outputs -- main and direct are in perfect phase. Analog inputs will only hit the ADC going into the recorder section.

The 664 automatically adds 1.7mS delay to the ADCs at the recorder inputs to ensure that the AES mic which has been summed into the mix matches phase-wise at the recorder section.

Any issues with delay differences between an AES mic and a regular analog mic is the same as what we work with daily since digital wireless systems came into regular use.

[pindrop]

So using a Schoeps super cmit

Latency

ch 1. 3.4 ms - processed by ILLUSONIC

ch 2. 1.6 ms - unprocessed digital CMIT

you'd be pretty much OK mixing in ch 2. but ch 1. would be problematic?

[Bob]

For all analog inputs, the path is completely analog inputs to outputs -- main and direct are in perfect phase. Analog inputs will only hit the ADC going into the recorder section.

The 664 automatically adds 1.7mS delay to the ADCs at the recorder inputs to ensure that the AES mic which has been summed into the mix matches phase-wise at the recorder section.

So to me this sounds like if you run a digital mic and an analog mic to the outputs so they can be recorded to camera it will be out of phase at that point since the ADC is only at the recorders inputs. The card tracks will be fine but the camera tracks will be screwed up.

Please someone correct me if I'm wrong because if this is the case that can be a huge issue.

[Bash]

Hi Matt, and thanks for illumination so far.

Perhaps I should ask the question another way....

If I plug an analogue mic into the 664, and have it routed to main OPs and also Aux OPs, and also Direct OP. Will all three of those OPs be timed the same, and a perect phase relationship?

If I now add a digital mic to the analogue mic, mix them evenly, and send the mix to the main OPs and the Aux OPs, will the mix be in a correct phase relationship? and will the main and Aux OPs still be timed correctly and in a good phase relationship.

Many thanks,

Simon B

[John Blankenship]

So to me this sounds like if you run a digital mic and an analog mic to the outputs so they can be recorded to camera it will be out of phase at that point since the ADC is only at the recorders inputs. The card tracks will be fine but the camera tracks will be screwed up.

Please someone correct me if I'm wrong because if this is the case that can be a huge issue.

Actually, it will be out of "time alignment." The phase alignment will vary with frequency.

[Bob]

Actually, it will be out of "time alignment." The phase alignment will vary with frequency.

So am I in the minority in thinking that this could be a problem?

[Tom Visser]

Use of a digital mic is going to introduce phase issues no matter what mixer is used unless there is per input delay compensation added, not anything specific to the 664.

[studiomprd]

" So am I in the minority in thinking that this could be a problem? "

I believe so...

[Philip Perkins]

I guess it depends on what the combo of analog and digital mics are hearing, ie how much of each others audio is in each channel. Seems sort of like the issues with combining digital or hybrid RX with older all analog RX--in some (most) situations they mix fine, but in a few you will hear coloration when you combine the two.

phil p

[John Blankenship]

Keep in mind that two mics, that both have an entirely analog signal flow, that are about 3-1/2 feet apart will have approximately the same difference in "time alignment" as two adjacent mics with one having about a 3ms digital delay.

[rofin]

Keep in mind that two mics, that both have an entirely analog signal flow, that are about 3-1/2 feet apart will have approximately the same difference in "time alignment" as two adjacent mics with one having about a 3ms digital delay.

Only if their radii from the sound source is different.

[pindrop]

Keep in mind that two mics, that both have an entirely analog signal flow, that are about 3-1/2 feet apart will have approximately the same difference in "time alignment" as two adjacent mics with one having about a 3ms digital delay.

Thanks John your post led me to find this calculator in to which temperature can also be plugged from the chart at the bottom

http://www.sengpielaudio.com/calculator-soundpath.htm

[Bob]

If I plug an analogue mic into the 664, and have it routed to main OPs and also Aux OPs, and also Direct OP. Will all three of those OPs be timed the same, and a perect phase relationship?

If I now add a digital mic to the analogue mic, mix them evenly, and send the mix to the main OPs and the Aux OPs, will the mix be in a correct phase relationship? and will the main and Aux OPs still be timed correctly and in a good phase relationship.

I think this is a very good question - yet still unanswered.