DAT-Heads Digest #48, Volume #3 Thu, 14 Nov 96 21:15:03 EST ----------------------------------------------------------------------------- From: Gianni Pavan Subject: SONY TCD-D7: anti-aliasing filter Date: Thu, 14 Nov 1996 23:04:56 +0100 Since I'm using DAT recorders for recording animal voices, and the SONY TCD-D7 is nice and small enough to be carried everywhere, I made some tests about its anti-alising filter and compared the results with those obtained with other machines I currently use. PROCEDURE: I tested the anti-alising filter of the SONY TCD-D7 by recording a sinusoidal tone sweeping from 1 kHz to 40 kHz. First I set up the signal generator to output 6Vpp, then I connected the output of the generator to the LINE inputs and I set the REC LEVEL exactly to 0dB. Then I reduced the generator output to 1.5Vpp to record at exactly -12dB. Then, I reduced the output level to 2.5mVpp to repeat the test with the MIC inputs (H setting). To verify the recording, I played back the tape on a DAT player with digital outputs digitally connected to a sound board with digital inputs (Audiologic AudioBoard Plus, made in Italy). Spectrograms were made up to the Nyquist frequency (24kHz) with custom software. A further control was made by acquiring and analyzing the analog output of the player with a high-speed sampling board (test made at 200ks/sec to check output frequencies up to 100kHz). RESULTS: The filters in the TCD-D7 are not steep. The roll-off begin smoothly at about 22 kHz; the "zero" of the filter is at about 31.5 kHz (considering "zero" an attenuation of -72dB referred to the input level) and thus, in the spectrograms, frequencies in the range 24kHz - 31.5 kHz are "reflected down" by the aliasing. This means that the frequency range 16.5kHz - 24 kHz may be "polluted" by aliasing when the input signal contains frequencies higher than 24kHz. Results from line input and mic input are identical. OTHER MACHINES: A similar result was obtained with the old portable CASIO DA2. Better results were obtained with the Technics SV260 (portable) and the Technics SV360 (the player used for the analyses): in these machines the slope of the filter is steeper and the "zero" is at about 26kHz. I also tested the Sound Blaster 32PnP sound board with a sampling frequency of 32000s/sec (since the SB does not sample at 48ks/sec) and I get results very similar to those obtained by the TCD-D7 running at 32ks/sec. -------------- I would greatly appreciate any information on other machines (somebody already tested the 96kHz Pioneer DATs or the new SONY TD-D8 ?) and further comments about this critical matter. ============================================================== Dr Gianni Pavan Centro Interdisciplinare di Bioacustica e Ricerche Ambientali Universita' degli Studi di Pavia Via Taramelli 24 27100 PAVIA, ITALIA Tel/Fax +39-382-525234 Email gpavan@telnetwork.it Web http://www.unipv.it/~webcib/welcome.html ============================================================== From: Dupre@avab.com (Joseph M. Dupre) Subject: D7 Self-noise Date: Tue, 01 Jul 97 9:41:49 -0008 I did some tests last night to analyze the self-noise of the Sony D7 and the microphones that I use. I was suprised to discover the following: 1) The self-noise of 'stealth' microphones is negligible when compared to the self-noise of the D7 itself. 2) The D7 produces an enormous amount of noise from 0 - 1500Hz centered at about 380Hz. (Although I think that this is mostly inaudible in most recording environments) 3) The D7's noise is essentially flat from 1500 - 22,000Hz (With a small disturbance at 14,800 when using line in) There are details and some fancy graphs of the results at http://207.88.40.213/wired/noisetest.htm Any comments on my procedure or analysis are welcomed. - Joe