Programmable Digital Audio Processor: Symetrix 322

[AB2EZ]

I bought one of these on eBay... new in the box... for about half the suggested retail price. I paid $269.00

http://symetrixaudio.com/index.php?Show=14&Show1=&Show2=257&Language=English

It is a 2-channel digital audio processor. Analog in and Analog out on each channel. It uses a high level GUI-based programming language to enable you to select the processing block's you want for each channel. Each channel can be used independently. The processing blocks you can chose (simple click and drag) include: multi-band compressors, low pass filters, high pass filters, parametric equalizers, pure delay (particularly useful when used in conjunction with Flex Radio products for aligning, in time, the input audio and the modulated output), and others functions.

I use one channel as a pure delay, and the other channel as an alternative audio chain: two 24dB/octave low pass filters in tandem to provide a 48dB per octave roll-off at whatever frequency I enter, two multi-band compressors (one with a higher threshold, but a higher degree of compression), an a multi-band parametric equalizer.

You program the box using your computer... but after you program it, it will store the program and run independently (you can unplug the computer from the box).

I find it to be more flexible (more features that you can use and more parameter values that you can set) than a 532E... with two independent channels, and at half the price of a 532E (if you buy it on eBay). It is also just 1 rack unit high and 1/2 rack width.

You can get a feel for it by downloading the free application software from Symetrix... and playing with the GUI.

Stu

[WA1QHQ]

Stu,

What is the latency of the audio through the processor, do you monitor your audio off the air?

Mark WA1QHQ

[AB2EZ]

Mark

Hi!

I monitor my audio off the air... and I can detect no latency (i.e., the latency is so small, that I do not notice it).

As an aside:

As you know (but as a clarification for others who may be reading this post) latency in digital signal processing is primarily caused very steep brick wall filters (steepness, not depth). As a rough rule of thumb: if a filter (whether digital of analog) transitions from no attenuation to high attenuation in 50 Hz, then it must have at least 20 milliseconds of delay (delay>1/the frequency change associated with the transition). It is only with the advent of modern digital signal processing that we are seeing boxes that implement such steep low pass filters (for example). On the other hand, if a filter (whether digital or analog) transitions from no attenuation at 5kHz to 24 dB of attenuation in 7kHz (48 dB/octave), then it must have (using the rough rule of thumb) at least (1/2500) seconds of delay =  0.4 milliseconds delay.... a much less significant lower bound on the latency from the perspective of things like monitoring one's own transmitted signal. 

Each channel in the 322 can include up to two low pass filters (in tandem)... each of which can have either 12dB per octave or 24 dB per octave of rolloff. I am using two filters in tandem, each set for 24dB per octave... with whatever cutoff frequency I decide to use at the time ... and therefore I am using a 48dB per octave rolloff.

[DMOD]

Hi Stu,

What is the latency of the audio through the processor, do you monitor your audio off the air?

I take it has at least a 192kHz internal sampling rate?   

Phil - AC0OB

[AB2EZ]

Symetrix does not provide a lot of details regarding the implementation... but piecing together various statements made on their FAQ page, etc. I believe the the A/D and D/A converters are operating at 48 kHz (with 24 bits of accuracy).

The latency is lower-bounded the sampling rate (48 kHz) and the number of samples in the FFT.

Latency> # samples in the FFT /sampling rate
Minimum frequency change resolution (e.g. sharpness of filters) =  sampling rate/# samples in the FFT

Symetrix (in the FAQ for the 322) says:

What is the latency of a Symetrix 322 DSP Engine?

Depending on the active DSP modules programmed into the signal path, the latency from analog-in to analog-out will be approximately between 1.7 milliseconds and 6.5 milliseconds.


If one uses 1.333 milliseconds as the minimum latency... and if one assumes that the sampling rate is 48 kHz, then the size of the FFT is .001333 x 48000 = 64 samples